Method and apparatus for wide bandwidth PPDU transmission in a high efficiency wireless LAN

ABSTRACT

Methods and apparatus for a wideband Physical layer Protocol Data Unit (PPDU) transmission in a High Efficiency WLAN (HEW) include a method for transmitting a Physical layer Protocol Data Unit (PPDU) in a wireless local area network. The method may further include performing a stream parsing of data bit streams to output blocks, determining whether to perform a segment parsing of the blocks based on a predetermined condition to output frequency subblocks, performing a constellation mapping of the blocks or the frequency subblocks, and transmitting the PPDU.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/983,247, filed Dec. 29, 2015, which application claims the benefitsof U.S. Provisional Application No. 62/098,256, filed on Dec. 30, 2014,and U.S. Provisional Application No. 62/264,559, filed on Dec. 8, 2015,which are hereby incorporated by reference as if fully set forth herein.

BACKGROUND Technical Field

The present disclosure relates to Wireless Local Area Networks (WLANs),and more particularly, to a method and apparatus for a wideband Physicallayer Protocol Data Unit (PPDU) transmission in a High Efficiency WLAN(HEW).

Related Art

Along with the recent development of information and telecommunicationtechnology, various wireless communication techniques have beendeveloped. Among them, the WLAN enables a user to wirelessly access theInternet based on radio frequency technology in a home, an office, or aspecific service area using a portable terminal such as a PersonalDigital Assistant (PDA), a laptop computer, a Portable Multimedia Player(PMP), a smartphone, etc.

To overcome limitations in communication speed that the WLAN faces, therecent technical standards have introduced a system that increases thespeed, reliability, and coverage of a wireless network. For example, theInstitute of Electrical and Electronics Engineers (IEEE) 802.11nstandard has introduced Multiple Input Multiple Output (MIMO) that isimplemented using multiple antennas at both a transmitter and a receiverin order to support High Throughput (HT) at a data processing rate of upto 540 Mbps, minimize transmission errors, and optimize data rates.

In recent times, to support increased numbers of devices supportingWLAN, such as smartphones, more Access Points (APs) have been deployed.Despite increase in use of WLAN devices supporting the Institute ofElectrical and Electronics Engineers (IEEE) 802.11ac standard, thatprovide high performance relative to WLAN devices supporting the legacyIEEE 802.11g/n standard, a WLAN system supporting higher performance isrequired due to WLAN users' increased use of high volume content such asa ultra high definition video. Although a conventional WLAN system hasaimed at increase of bandwidth and improvement of a peak transmissionrate, actual users thereof could not feel drastic increase of suchperformance.

In a task group called IEEE 802.11ax, High Efficiency WLAN (HEW)standardization is under discussion. The HEW aims at improvingperformance felt by users demanding high-capacity, high-rate serviceswhile supporting simultaneous access of numerous stations in anenvironment in which a plurality of APs is densely deployed and coverageareas of APs overlap.

However, there is no specified method for a wideband PPDU transmissionin a HEW.

SUMMARY

The present disclosure describes embodiments of a method and apparatusfor a wideband PPDU transmission in a HEW.

The embodiments contemplated by the present disclosure are not limitedto the foregoing descriptions, and additional embodiments will becomeapparent to those having ordinary skill in the pertinent art to thepresent disclosure based upon the following descriptions.

In an aspect of the present disclosure, a method for transmitting aPhysical layer Protocol Data Unit (PPDU) in a wireless local areanetwork may be provided. The method may include performing a streamparsing of data bit streams to output blocks; determining whether toperform a segment parsing of the blocks based on a predeterminedcondition to output frequency subblocks; and performing a constellationmapping of the blocks or the frequency subblocks and transmitting thePPDU.

In another aspect of the present disclosure, a method for receiving aPhysical layer Protocol Data Unit (PPDU) in a wireless local areanetwork may be provided. The method may include performing a Space-TimeBlock Coding (STBC) decoding of the PPDU to output blocks; determiningwhether to perform a segment parsing of the blocks based on apredetermined condition to output frequency subblocks; and performing aconstellation demapping of the blocks or the frequency subblocks.

In another aspect of the present disclosure, a transmitting apparatusfor transmitting a Physical layer Protocol Data Unit (PPDU) in awireless local area network may be provided. The transmitting apparatusmay include a baseband processor, a Radio Frequency (RF) transceiver, amemory, etc. The baseband processor may be configured to perform streamparsing of data bit streams to output blocks; determine whether toperform a segment parsing of the blocks based on a predeterminedcondition to output frequency subblocks; perform a constellation mappingof the blocks or the frequency subblocks; and transmitting the PPDU.

In another aspect of the present disclosure, a receiving apparatus forreceiving a Physical layer Protocol Data Unit (PPDU) in a wireless localarea network may be provided. The receiving apparatus may include abaseband processor, an RF transceiver, a memory, etc. The basebandprocessor may be configured to perform a Space-Time Block Coding (STBC)decoding of the PPDU to output blocks; determine whether to perform asegment parsing of the blocks based on a predetermined condition tooutput frequency subblocks; and perform a constellation demapping of theblocks or the frequency subblocks.

In another aspect of the present disclosure, a non-transitorycomputer-readable medium having instructions executable for atransmitting device to transmit a Physical layer Protocol Data Unit(PPDU) in a wireless local area network may be provided. The executableinstructions may cause the transmitting device to perform a streamparsing of data bit streams to output blocks; determine whether toperform a segment parsing of the blocks based on a predeterminedcondition to output frequency subblocks; perform a constellation mappingof the blocks or the frequency subblocks; and transmitting the PPDU.

In another aspect of the present disclosure, a non-transitorycomputer-readable medium having instructions executable for a receivingdevice to receive a Physical layer Protocol Data Unit (PPDU) in awireless local area network may be provided. The executable instructionsmay cause the receiving device to perform a Space-Time Block Coding(STBC) decoding of the PPDU to output blocks; determine whether toperform a segment parsing of the blocks based on a predeterminedcondition to output frequency subblocks; and perform a constellationdemapping of the blocks or the frequency subblocks.

It is to be understood that the foregoing summarized features areexample aspects of the following detailed description of the presentdisclosure and are not intended to limit the scope of the presentdisclosure.

According to the present disclosure, a method and apparatus for awideband PPDU transmission in a HEW can be provided.

The advantages of the present disclosure are not limited to theforegoing descriptions, and additional advantages will become apparentto those having ordinary skill in the pertinent art to the presentdisclosure based upon the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the disclosure andtogether with the description serve to explain the principle of thedisclosure. In the drawings:

FIG. 1 is a block diagram of a Wireless Local Area Network (WLAN)device.

FIG. 2 is a schematic block diagram of an example transmitting signalprocessing unit in a WLAN.

FIG. 3 is a schematic block diagram of an example receiving signalprocessing unit in a WLAN.

FIG. 4 depicts a relationship between InterFrame Spaces (IFSs).

FIG. 5 is a conceptual diagram illustrating a procedure for transmittinga frame in Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA) for avoiding collisions between frames in a channel.

FIG. 6 depicts an example frame structure in a WLAN system.

FIG. 7 depicts an example HE PPDU frame format.

FIG. 8 depicts an example High Efficiency (HE) Physical layer ProtocolData Unit (PPDU) frame format according to the present disclosure.

FIG. 9 depicts subchannel allocation in an HE PPDU frame formataccording to the present disclosure.

FIG. 10 depicts a subchannel allocation method according to the presentdisclosure.

FIG. 11 depicts the starting and ending points of a High Efficiency LongTraining Field (HE-LTF) field in an HE PPDU frame format according tothe present disclosure.

FIG. 12 depicts a High Efficiency SIGnal B (HE-SIG-B) field and a HighEfficiency SIGnal C (HE-SIG-C) field in the HE PPDU frame formataccording to the present disclosure.

FIG. 13 depicts another example of an HE PPDU frame format according tothe present disclosure.

FIG. 14 depicts an example HE PPDU frame format for a wide channel bandaccording to the present disclosure.

FIG. 15 depicts another example HE PPDU frame format according to thepresent disclosure.

FIGS. 16 and 17 depict operating channels in a WLAN system.

FIGS. 18 and 19 are block diagrams of a transmitting signal processingunit for wideband PPDU transmission.

FIG. 20 is a flowchart depicting a method for processing a transmissionsignal for wideband PPDU transmission according to an example of thepresent disclosure.

FIG. 21 is a flowchart depicting a method for processing a receivedsignal, for wideband PPDU reception according to an example of thepresent disclosure.

FIGS. 22 and 23 depict example HE PPDU formats in the case where OFDMAtransmission is performed using a wideband channel bandwidth.

FIG. 24 depicts an example channel access operation for wideband OFDMAPPDU transmission.

FIG. 25 is a flowchart depicting a method for determining a transmissionbandwidth for wideband PPDU transmission according to an example of thepresent disclosure.

FIG. 26 depicts another example of a channel access operation forwideband OFDMA PPDU transmission.

FIG. 27 is a block diagram of a transmitting signal processing unit forOFDMA PPDU transmission according to the present disclosure.

DETAILED DESCRIPTION

In the following detailed description, certain embodiments of thepresent disclosure have been shown and described, by way ofillustration. As those skilled in the art would realize, the describedembodiments may be modified in various different ways, without departingfrom the spirit or scope of the present disclosure. Accordingly, thedrawings and description are to be regarded as illustrative in natureand not restrictive. Like reference numerals designate like elementsthroughout the present disclosure.

In a Wireless Local Area network (WLAN), a Basic Service Set (BSS)includes a plurality of WLAN devices. A WLAN device may include a MediumAccess Control (MAC) layer and a PHYsical (PHY) layer according toInstitute of Electrical and Electronics Engineers (IEEE) 802.11 seriesstandards. In the plurality of WLAN devices, at least one the WLANdevice may be an Access Point (AP) and the other WLAN devices may benon-AP Stations (non-AP STAs). Alternatively, all of the plurality ofWLAN devices may be non-AP STAs in an ad-hoc networking environment. Ingeneral, AP STA and non-AP STA may be each referred to as a STA or maybe collectively referred to as STAs. However, for ease of descriptionherein, only the non-AP STAs may be referred to herein as STAs.

FIG. 1 is a block diagram of a WLAN device.

Referring to FIG. 1, a WLAN device 1 includes a baseband processor 10, aRadio Frequency (RF) transceiver 20, an antenna unit 30, a memory 40,which may be or may include a non-transitory computer-readable medium,an input interface unit 50, an output interface unit 60, and a bus 70.

The baseband processor 10 may be simply referred to as a processor, andmay perform baseband signal processing described in the presentdisclosure, and includes a MAC processor (or MAC entity) 11 and a PHYprocessor (or PHY entity) 15.

In an embodiment of the present disclosure, the MAC processor 11 mayinclude a MAC software processing unit 12 and a MAC hardware processingunit 13. The memory 40 may store software or machine-executableinstructions (hereinafter referred to as ‘MAC software’) including atleast some functions of the MAC layer. The MAC software processing unit12 may execute the MAC software to implement some functions of the MAClayer, and the MAC hardware processing unit 13 may implement theremaining functions of the MAC layer as hardware (hereinafter referredto as ‘MAC hardware’). However, embodiments of the MAC processor 11 arenot limited to this distribution of functionality.

The PHY processor 15 includes a transmitting (TX) signal processing unit100 and a receiving (RX) signal processing unit 200.

The baseband processor 10, the RF transceiver 20, the memory 40, theinput interface unit 50, and the output interface unit 60 maycommunicate with one another via the bus 70.

The RF transceiver 20 includes an RF transmitter 21 and an RF receiver22.

The memory 40 may further store an Operating System (OS) andapplications. The input interface unit 50 receives information from auser, and the output interface unit 60 outputs information to the user.

The antenna unit 30 includes one or more antennas. When Multiple InputMultiple Output (MIMO) or Multi-User MIMO (MU-MIMO) is used, the antennaunit 30 may include a plurality of antennas.

FIG. 2 is a schematic block diagram of an example transmitting signalprocessor in a WLAN.

Referring to FIG. 2, the transmitting signal processing unit 100 mayinclude an encoder 110, an interleaver 120, a mapper 130, an InverseFourier Transformer (IFT) 140, and a Guard Interval (GI) inserter 150.

The encoder 110 encodes input data. For example, the encoder 100 may bea Forward Error Correction (FEC) encoder. The FEC encoder may include aBinary Convolutional Code (BCC) encoder followed by a puncturing device,or the FEC encoder may include a Low-Density Parity-Check (LDPC)encoder.

The transmitting signal processing unit 100 may further include ascrambler for scrambling the input data before encoding to reduce theprobability of long sequences of Os or Is. If BCC encoding is used inthe encoder 110, the transmitting signal processing unit 100 may furtherinclude an encoder parser for demultiplexing the scrambled bits among aplurality of BCC encoders. If LDPC encoding is used in the encoder 110,the transmitting signal processing unit 100 may not use the encoderparser.

The interleaver 120 interleaves the bits of each stream output from theencoder 110 to change the order of bits. Interleaving may be appliedwhen BCC encoding is used in the encoder 110. The mapper 130 maps thesequence of bits output from the interleaver 120 to constellationpoints. If LDPC encoding is used in the encoder 110, the mapper 130 mayfurther perform LDPC tone mapping in addition to constellation mapping.

When MIMO or MU-MIMO is used, the transmitting signal processing unit100 may use a plurality of interleavers 120 and a plurality of mappers130 corresponding to the number of spatial streams, N_(SS). In thiscase, the transmitting signal processing unit 100 may further include astream parser for dividing outputs of the BCC encoders or output of theLDPC encoder into blocks that are sent to different interleavers 120 ormappers 130. The transmitting signal processing unit 100 may furtherinclude a Space-Time Block Code (STBC) encoder for spreading theconstellation points from the N_(SS) spatial streams into N_(STS)space-time streams and a spatial mapper for mapping the space-timestreams to transmit chains. The spatial mapper may use direct mapping,spatial expansion, or beamforming.

The IFT 140 converts a block of constellation points output from themapper 130 or the spatial mapper to a time-domain block (i.e., a symbol)by using Inverse Discrete Fourier Transform (IDFT) or Inverse FastFourier Transform (IFFT). If the STBC encoder and the spatial mapper areused, the IFT 140 may be provided for each transmit chain.

When MIMO or MU-MIMO is used, the transmitting signal processing unit100 may insert Cyclic Shift Diversities (CSDs) to prevent unintentionalbeamforming. The CSD insertion may occur before or after IFT. The CSDmay be specified per transmit chain or may be specified per space-timestream. Alternatively, the CSD may be applied as a part of the spatialmapper.

When MU-MIMO is used, some blocks before the spatial mapper may beprovided for each user.

The GI inserter 150 prepends a GI to the symbol. The transmitting signalprocessing unit 100 may optionally perform windowing to smooth edges ofeach symbol after inserting the GI. The RF transmitter 21 converts thesymbols into an RF signal and transmits the RF signal via the antennaunit 30. When MIMO or MU-MIMO is used, the GI inserter 150 and the RFtransmitter 21 may be provided for each transmit chain.

FIG. 3 is a schematic block diagram of an example receiving signalprocessor in a WLAN.

Referring to FIG. 3, the receiving signal processing unit 200 includes aGI remover 220, a Fourier Transformer (FT) 230, a demapper 240, adeinterleaver 250, and a decoder 260.

An RF receiver 22 receives an RF signal via the antenna unit 30 andconverts the RF signal into one or more symbols. The GI remover 220removes the GI from the symbol. When MIMO or MU-MIMO is used, the RFreceiver 22 and the GI remover 220 may be provided for each receivechain.

The FT 230 converts the symbol (i.e., the time-domain block) into ablock of constellation points by using a Discrete Fourier Transform(DFT) or a Fast Fourier Transform (FFT). The FT 230 may be provided foreach receive chain.

When MIMO or MU-MIMO is used, the receiving signal processing unit 200may use/include a spatial demapper for converting Fourier Transformedreceiver chains to constellation points of the space-time streams, andan STBC decoder for despreading the constellation points from thespace-time streams into the spatial streams.

The demapper 240 demaps the constellation points output from the FT 230or the STBC decoder to bit streams. If LDPC encoding is applied to thereceived signal, the demapper 240 may further perform LDPC tonedemapping before constellation demapping. The deinterleaver 250deinterleaves the bits of each stream output from the demapper 240.Deinterleaving may be applied when a BCC encoding scheme is applied tothe received signal.

When MIMO or MU-MIMO is used, the receiving signal processing unit 200may use a plurality of demappers 240 and a plurality of deinterleavers250 corresponding to the number of spatial streams. In this case, thereceiving signal processing unit 200 may further include a streamdeparser for combining streams output from the deinterleavers 250.

The decoder 260 decodes the streams output from the deinterleaver 250 orthe stream deparser. For example, the decoder 100 may be an FEC decoder.The FEC decoder may include a BCC decoder or an LDPC decoder. Thereceiving signal processing unit 200 may further include a descramblerfor descrambling the decoded data. If BCC decoding is used in thedecoder 260, the receiving signal processing unit 200 may furtherinclude an encoder deparser for multiplexing the data decoded by aplurality of BCC decoders. If LDPC decoding is used in the decoder 260,the receiving signal processing unit 200 may not use the encoderdeparser.

In a WLAN system, Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA) is a basic MAC access mechanism. The CSMA/CA mechanism isreferred to as Distributed Coordination Function (DCF) of IEEE 802.11MAC, or colloquially as a ‘listen before talk’ access mechanism.According to the CSMA/CA mechanism, an AP and/or a STA may sense amedium or a channel for a predetermined time before startingtransmission, that is, the AP and/or the STA may perform Clear ChannelAssessment (CCA). If the AP or the STA determines that the medium orchannel is idle, it may start to transmit a frame on the medium orchannel. On the other hand, if the AP and/or the STA determines that themedium or channel is occupied or busy, it may set a delay period (e.g.,a random backoff period), wait for the delay period without startingtransmission, and then attempt to transmit a frame. By applying a randombackoff period, a plurality of STAs are expected to attempt frametransmission after waiting for different time periods, resulting in lesscollisions.

FIG. 4 depicts a relationship between InterFrame Spaces (IFSs).

WLAN devices may exchange data frames, control frames, and managementframes with each other.

A data frame is used for transmission of data forwarded to a higherlayer. The WLAN device transmits the data frame after performing backoffif a Distributed Coordination Function IFS (DIFS) has elapsed from atime when the medium has been idle. A management frame is used forexchanging management information which is not forwarded to the higherlayer. The WLAN device transmits the management frame after performingbackoff if an IFS such as the DIFS or a Point Coordination Function IFS(PIFS) has elapsed. Subtype frames of the management frame include abeacon frame, an association request/response frame, a proberequest/response frame, and an authentication request/response frame. Acontrol frame is used for controlling access to the medium. Subtypeframes of the control frame include a Request-To-Send (RTS) frame, aClear-To-Send (CTS) frame, and an ACKnowledgement (ACK) frame. In thecase that the control frame is not a response frame to a previous frame,the WLAN device transmits the control frame after performing backoff ifthe DIFS has elapsed. In case that the control frame is a response frameto a previous frame, the WLAN device transmits the control frame withoutperforming backoff if a Short IFS (SIFS) has elapsed. The type andsubtype of a frame may be identified by a type field and a subtype fieldin a Frame Control (FC) field.

On the other hand, a Quality of Service (QoS) STA transmits a frameafter performing backoff if an Arbitration IFS (AIFS) for an associatedAccess Category (AC), i.e., AIFS[i] (i is determined based on AC) haselapsed. In this case, the AIFC[i] may be used for a data frame, amanagement frame, or a control frame that is not a response frame.

In the example illustrated in FIG. 4, upon generation of a frame to betransmitted, a STA may transmit the frame immediately, if it determinesthat the medium is idle for the DIFS or AIFS[i] or longer. The medium isbusy for a time period during which the STA transmits the frame. Duringthe time period, upon generation of a frame to be transmitted, anotherSTA may defer access by confirming that the medium is busy. If themedium is idle, the STA that intends to transmit the frame may perform abackoff operation after a predetermined IFS in order to minimizecollision with any other STA. Specifically, the STA that intends totransmit the frame selects a random backoff count, waits for a slot timecorresponding to the selected random backoff count, and then attemptstransmission. The random backoff count is determined based on aContention Window (CW) parameter and the medium is monitoredcontinuously during count-down of backoff slots (i.e. decrement abackoff count-down) according to the determined backoff count. If theSTA monitors the medium as busy, the STA discontinues the count-down andwaits, and then, if the medium gets idle, the STA resumes thecount-down. If the backoff slot count reaches 0, the STA may transmitthe next frame.

FIG. 5 is a conceptual diagram illustrating a CSMA/CA-based frametransmission procedure for avoiding collisions between frames in achannel.

Referring FIG. 5, a first STA (STA1) is a transmit WLAN device fortransmitting data, a second STA (STA2) is a receive WLAN device forreceiving the data from STA1, and a third STA (STA3) is a WLAN devicewhich may be located in an area where a frame transmitted from STA1and/or a frame transmitted from STA2 can be received by STA3.

STA1 may determine whether the channel is busy by carrier sensing. TheSTA1 may determine the channel occupation based on an energy level onthe channel or correlation of signals in the channel, or may determinethe channel occupation by using a Network Allocation Vector (NAV) timer.

After determining that the channel is not being used by other devicesduring DIFS (that is, the channel is idle), STA1 may transmit an RTSframe to STA2 after performing backoff. Upon receiving the RTS frame,STA2 may transmit a CTS frame as a response to the CTS frame after SIFS.

When STA3 receives the RTS frame, STA3 may set the NAV timer for atransmission duration of subsequently transmitted frame by usingduration information included in the RTS frame. For example, the NAVtimer may be set for a duration of SIFS+CTS frame duration+SIFS+dataframe duration+SIFS+ACK frame duration. When STA3 receives the CTSframe, it may set the NAV timer for a transmission duration ofsubsequently transmitted frames by using duration information includedin the CTS frame. For example, the NAV timer may be set for a durationof SIFS+a data frame duration+SIFS+an ACK frame duration. Upon receivinga new frame before the NAV timer expires, STA3 may update the NAV timerby using duration information included in the new frame. STA3 does notattempt to access the channel until the NAV timer expires.

When STA1 receives the CTS frame from STA2, it may transmit a data frameto STA2 after SIFS elapsed from the CTS frame has been completelyreceived. Upon successfully receiving the data frame, STA2 may transmitan ACK frame as a response to the data frame after SIFS elapsed.

When the NAV timer expires, STA3 may determine whether the channel isbusy through the use of carrier sensing. Upon determining that thechannel is not in use by other devices during DIFS and after the NAVtimer has expired, STA3 may attempt channel access after a contentionwindow after a random backoff has elapsed.

FIG. 6 depicts an example frame structure in a WLAN system.

PHY layer may prepare for transmission of a MAC PDU (MPDU) in responseto an instruction (or a primitive, which is a set of instructions or aset of parameters) by the MAC layer. For example, upon receipt of aninstruction requesting transmission start from the MAC layer, the PHYlayer may switch to a transmission mode, construct a frame withinformation (e.g., data) received from the MAC layer, and transmit theframe.

Upon detection of a valid preamble in a received frame, the PHY layermonitors a header of the preamble and transmits an instructionindicating reception start of the PHY layer to the MAC layer.

Information is transmitted and received in frames in the WLAN system.For this purpose, a Physical layer Protocol Data Unit (PPDU) frameformat is defined.

A PPDU frame may include a Short Training Field (STF) field, a LongTraining Field (LTF) field, a SIGNAL (SIG) field, and a Data field. Themost basic (e.g., a non-High Throughput (non-HT)) PPDU frame may includeonly a Legacy-STF (L-STF) field, a Legacy-LTF (L-LTF) field, a SIGfield, and a Data field. Additional (or other types of) STF, LTF, andSIG fields may be included between the SIG field and the Data fieldaccording to the type of PPDU frame format (e.g., an HT-mixed formatPPDU, an HT-greenfield format PPDU, a Very High Throughput (VHT) PPDU,etc.).

The STF is used for signal detection, Automatic Gain Control (AGC),diversity selection, fine time synchronization, etc. The LTF field isused for channel estimation, frequency error estimation, etc. The STFand the LTF fields may be referred to as signals for OFDM PHY layersynchronization and channel estimation.

The SIG field may include a RATE field and a LENGTH field. The RATEfield may include information about a modulation scheme and coding rateof data. The LENGTH field may include information about the length ofthe data. The SIG field may further include parity bits, SIG TAIL bits,etc.

The Data field may include a SERVICE field, a Physical layer ServiceData Unit (PSDU), and PPDU TAIL bits. When needed, the Data field mayfurther include padding bits. Some of the bits of the SERVICE field maybe used for synchronization at a descrambler of a receiver. The PSDUcorresponds to a MAC PDU defined at the MAC layer and may include datagenerated/used in a higher layer. The PPDU TAIL bits may be used toreturn an encoder to a zero state. The padding bits may be used to matchthe length of the Data filed in predetermined units.

A MAC PDU is defined according to various MAC frame formats. A basic MACframe includes a MAC header, a frame body, and a Frame Check Sequence(FCS). The MAC frame includes a MAC PDU and may be transmitted andreceived in the PSDU of the data part in the PPDU frame format.

The MAC header includes a Frame Control field, a Duration/Identifier(ID) field, an Address field, etc. The Frame Control field may includecontrol information required for frame transmission/reception. TheDuration/ID field may be set to a time for transmitting the frame. Fordetails of Sequence Control, QoS Control, and HT Control subfields ofthe MAC header, refer to the IEEE 802.11-2012 technical specification,which is hereby incorporated by reference.

The Frame Control field of the MAC header may include Protocol Version,Type, Subtype, To Distribution System (DS), From DS, More Fragment,Retry, Power Management, More Data, Protected Frame, and Ordersubfields. For the contents of each subfield in the Frame Control field,refer to the IEEE 802.11-2012 technical specification.

A Null-Data Packet (NDP) frame format is a frame format that does notinclude a data packet. In other words, the NDP frame format includes aPhysical Layer Convergence Protocol (PLCP) header part (i.e., the STF,LTF, and SIG fields) of the general PPDU frame format, without theremaining part (i.e., the Data field) of the general PPDU frame format.The NDP frame format may be referred to as a short frame format.

The IEEE 802.11ax task group is discussing a WLAN system, called a HighEfficiency WLAN (HEW) system, that operates in 2.4 GHz or 5 GHz andsupports a channel bandwidth (or channel width) of 20 MHz, 40 MHz, 80MHz, or 160 MHz. The present disclosure defines a new PPDU frame formatfor the IEEE 802.1 lax HEW system. The new PPDU frame format may supportMU-MIMO or OFDMA. A PPDU of the new format may be referred to as a ‘HEWPPDU’ or ‘HE PPDU’ (similarly, HEW xyz may be referred to as ‘HE xyz’ or‘HE-xyz’ in the following descriptions).

In present disclosure, the term ‘MU-MIMO or OFDMA mode’ includes MU-MIMOwithout using OFDMA, or OFDMA mode without using MU-MIMO in anorthogonal frequency resource, or OFDMA mode using MU-MIMO in anorthogonal frequency resource.

FIG. 7 depicts an example HE PPDU frame format.

A transmitting STA may generate a PPDU frame according to the HE PPDUframe format as illustrated in FIG. 7 and transmit the PPDU frame to areceiving STA. The receiving STA may receive, detect, and process thePPDU.

The HE PPDU frame format may broadly include two parts: the first partincluding an L-STF field, an L-LTF field, an L-SIG field, a RepeatedL-SIG (RL-SIG) field, an HE-SIG-A field, and an HE-SIG-B field and thesecond part including an HE-STF field, an HE-LTF field, and an HE-DATAfield. 64-FFT based on a channel bandwidth of 20 MHz may be applied tothe first part and a basic subcarrier spacing of 312.5 kHz and a basicDFT period of 3.2 μs may be included in the first part. 256-FFT based ona channel bandwidth of 20 MHz may be applied to the second part and abasic subcarrier spacing of 75.125 kHz and a basic DFT period of 12.8 μsmay be included in the second part.

The HE-SIG-A field may include N_(HESIGA) symbols, the HE-SIG-B fieldmay include N_(HESIGB) symbols, the HE-LTF field may include N_(HELTF)symbols, and the HE-DATA field may include N_(DATA) symbols.

A detailed description of the fields included in the HE PPDU frameformat is given in Table I.

TABLE I DFT Subcarrier Element definition duration period GI spacingDescription Legacy(L)- Non-high 8 μs — — equivalent to L-STF of anon-trigger-based STF throughput(HT) 1,250 kHz PPDU has a periodicity of0.8 μs Short Training with 10 periods. field L-LTF Non-HT Long 8 μs 3.2μs 1.6 μs 312.5 kHz Training field L-SIG Non-HT 4 μs 3.2 μs 0.8 μs 312.5kHz SIGNAL field RL-SIG Repeated Non- 4 μs 3.2 μs 0.8 μs 312.5 kHz HTSIGNAL field HE-SIG-A HE SIGNAL A H_(HESIGA) * 3.2 μs 0.8 μs 312.5 kHzHE-SIG-A is duplicated on each field 4 μs 20 MHz segment after thelegacy preamble to indicate common control information. N_(HESIGA) meansthe number of OFDM symbols of the HE-SIG-A field and is equal to 2 or 4.HE-SIG-B HE SIGNAL B H_(HESIGB) * 3.2 μs 0.8 μs 312.5 kHz N_(HESIGB)means the number of field 4 μs OFDM symbols of the HE-SIG-B field and isvariable. DL MU packet contains HE-SIG- B. SU packets and UL Triggerbased packets do not contain HE-SIG-B. HE-STF HE Short 4 or 8 μs — —non- HE-STF of a non-trigger-based Training field trigger- PPDU has aperiodicity of 0.8 μs based with 5 periods. A non-trigger-based PPDU:PPDU is not sent in response to a (equivalent trigger frame. to) 1,250kHz; The HE-STF of a trigger-based trigger- PPDU has a periodicity of1.6 μs based with 5 periods. A trigger-based PPDU: PPDU is an UL PPDUsent in (equivalent response to a trigger frame. to) 625 kHz HE-STF HELong H_(HELTF) * 2xLTF: supports 2xLTF: HE PPDU shall support 2xLTFTraining field (DTF 6.4 μs 0.8, 1.6, (equivalent mode and 4xLTF mode.period + 4xLTF: 3.2 μs to) 156.25 kHz; In the 2xLTF mode, HE-LTF GI) μs12.8 μs 4xLTF: symbol excluding GI is equivalent 78.125 kHz tomodulating every other tone in an OFDM symbol of 12.8 μs excluding GI,and then removing the second half of the OFDM symbol in time domain.N_(HELTF) means the number of HE- LTF symbols and is equal to 1, 2, 4,6, 8. HE-DATA HE DATA N_(DATA) * 12.8 μs supports 78.125 kHz  N_(DATA)means the number of HE field (DTF 0.8, 1.6, data symbols. period + 3.2μs GI) μs

L-STF is a non-HT Short Training field and may have a duration of 8 μsand a subcarrier spacing equivalent to 1250 kHz. L-STF of a PPDU whichis not based on a trigger may have a periodicity of 0.8 μs with 10periods. Herein, the trigger corresponds to scheduling information forUL transmission.

L-LTF is a non-HT Long Training field and may have a duration of 8 μs, aDFT period of 3.2 μs, a Guard Interval (GI) of 1.6 μs, and a subcarrierspacing of 312.5 kHz.

L-SIG is a non-HT SIGNAL field and may have a duration of 4 μs, a DFTperiod of 3.2 μs, a GI of 0.8 μs, and a subcarrier spacing of 312.5 kHz.

RL-SIG is a Repeated Non-HT SIGNAL field and may have a duration of 4μs, a DFT period of 3.2 μs, a GI of 0.8 μs, and a subcarrier spacing of312.5 kHz.

L-STF, L-LTF, L-SIG, and RL-SIG may be called legacy preambles.

HE-SIG-A is an HE SIGNAL A field and may have a duration of N_(HESIGA)*4μs, a DFT period of 3.2 μs, a GI of 0.8 μs, and a subcarrier spacing of312.5 kHz. HE-SIG-A may be duplicated on each 20 MHz segment after thelegacy preambles to indicate common control information. N_(HESIGA)represents the number of OFDM symbols of the HE-SIG-A field and may havea value of 2 or 4.

HE-SIG-B is an HE SIGNAL B field and may have a duration of N_(HESIGB)*4μs, a DFT period of 3.2 μs, a GI of 0.8 μs, and a subcarrier spacing of312.5 kHz. N_(HESIGB) represents the number of OFDM symbols of theHE-SIG-B field and may have a variable value. In addition, although a DLMulti-User (MU) packet may include the HE-SIG-B field, a Single-User(SU) packet and a UL trigger based packet may not include the HE-SIG-Bfield.

HE-STF is an HE Short Training field and may have a duration of 4 or 8μs. A non-trigger based PPDU may have a subcarrier spacing equivalent to1250 kHz and a trigger based PPDU may have a subcarrier spacingequivalent to 625 kHz. HE-STF of the non-triggered PPDU may have aperiodicity of 0.8 μs with 4 periods. The non-triggered PPDU is nottransmitted in response to a trigger field. HE-STF of the trigger basedPPDU may have a periodicity of 1.6 μs with 5 periods. The trigger basedPPDU is a UL PPDU transmitted in response to the trigger frame.

HE-LTF is an HE Long Training field and may have a duration ofN_(HELTF)*(DFT period+GI)μs. N_(HELTF) represents the number of HE-LTFsymbols and may have a value of 1, 2, 4, 6, or 8. An HE PPDU may supporta 2×LTF mode and a 4×LTF mode. In the 2×LTF mode, an HE-LTF symbolexcept for a GI is equivalent to a symbol obtained by modulating everyother tone in an OFDM symbol of 12.8 μs excluding a GI and theneliminating the first half or the second half of the OFDM symbol in thetime domain. In the 4×LTF mode, an HE-LTF symbol excluding a GI areequivalent to a symbol obtained by modulating every fourth tone in anOFDM symbol of 12.8 μs excluding a GI and then eliminating the firstthree-fourths or the last three-fourths of the OFDM symbol in the timedomain. 2×LTF may have a DFT period of 6.4 μs and 4×LTF may have a DFTperiod of 12.8 μs. A GI of HE-LTF may support 0.8 μs, 1.6 μs, and 3.2μs. 2×LTF may have a subcarrier spacing equivalent to 156.25 kHz and4×LTF may have a subcarrier spacing of 78.125 kHz.

HE-DATA is an HE DATA field and may have a duration of, N_(DATA)*(DFTperiod+GI)μs. N_(DATA) represents the number of HE-DATA symbols. HE-DATAmay have a DFT period of 12.8 μs. A GI of HE-DATA may support 0.8 μs,1.6 μs, and 3.2 μs. HE-DATA may have a subcarrier spacing of 78.125 kHz.

The above description of the fields included in the HE PPDU frame formatmay be combined with example HE PPDU frame formats described below. Forexample, characteristics of fields exemplarily described below may beapplied while a transmission order of the fields of the HE PPDU frameformat of FIG. 7 is maintained.

FIG. 8 depicts an example HE PPDU frame format according to the presentdisclosure.

Referring to FIG. 8, the vertical axis represents frequency and thehorizontal axis represents time. It is assumed that frequency and timeincrease in the upward direction and the right direction, respectively.

In the example of FIG. 8, one channel includes four subchannels. AnL-STF, an L-LTF, an L-SIG, and an HE-SIG-A may be transmitted perchannel (e.g., 20 MHz). An HE-STF and an HE-LTF may be transmitted oneach basic subchannel unit (e.g., 5 MHz)), and an HE-SIG-B and a PSDUmay be transmitted on each of the subchannels allocated to a STA. Asubchannel allocated to a STA may have a size required for PSDUtransmission to the STA. The size of the subchannel allocated to the STAmay be N (N=1, 2, 3, . . . ) times as large as the size of basicsubchannel unit (i.e., a subchannel having a minimum size). In theexample of FIG. 8, the size of a subchannel allocated to each STA isequal to the size of the basic subchannel unit. For example, a firstsubchannel may be allocated for PSDU transmission from an AP to STA1 andSTA2, a second subchannel may be allocated for PSDU transmission fromthe AP to STA3 and STA4, a third subchannel may be allocated for PSDUtransmission from the AP to STA5, and a fourth subchannel may beallocated for PSDU transmission from the AP to STA6.

While the term subchannel is used in the present disclosure, the termsubchannel may also be referred to as Resource Unit (RU) or subband. Inparticular, terms like OFDMA subchannel, OFDMA RU, OFDMA subband can beused as synonyms for OFDMA in the present disclosure. Terms like abandwidth of a subchannel, a number of tones (or subcarriers) allocatedto a subchannel, a number of data tones (or data subcarriers) allocatedto a subchannel can be used to express a size of a subchannel. Asubchannel refers to a frequency band allocated to a STA and a basicsubchannel unit refers to a basic unit used to represent the size of asubchannel. While the size of the basic subchannel unit is 5 MHz in theabove example, this is purely example. Thus, the basic subchannel unitmay have a size of 2.5 MHz.

In FIG. 8, a plurality of HE-LTF elements are distinguished in the timeand frequency domains. One HE-LTF element may correspond to one OFDMsymbol in time domain and one subchannel unit (i.e., a subchannelbandwidth allocated to a STA) in frequency domain. The HE-LTF elementsare logical units, and the PHY layer does not necessarily operate inunits of an HE-LTF element. In the following description, an HE-LTFelement may be referred to shortly as an HE-LTF.

An HE-LTF symbol may correspond to a set of HE-LTF elements in one OFDMsymbol in time domain and in one channel unit (e.g., 20 MHz) infrequency domain.

An HE-LTF section may correspond to a set of HE-LTF elements in one ormore OFDM symbols in time domain and in one subchannel unit (i.e., asubchannel bandwidth allocated to a STA) in frequency domain.

An HE-LTF field may be a set of HE-LTF elements, HE-LTF symbols, orHE-LTF sections for a plurality of STAs.

The L-STF field is used for frequency offset estimation and phase offsetestimation, for preamble decoding at a legacy STA (i.e., a STA operatingin a system such as IEEE 802.11a/b/g/n/ac). The L-LTF field is used forchannel estimation, for the preamble decoding at the legacy STA. TheL-SIG field is used for the preamble decoding at the legacy STA andprovides a protection function for PPDU transmission of a third-partySTA (e.g., a third-party STA is not allowed to transmit during a certainperiod based on the value of a LENGTH field included in the L-SIGfield).

HE-SIG-A (or HEW SIG-A) represents High Efficiency Signal A (or HighEfficiency WLAN Signal A), and includes HE PPDU (or HEW PPDU) modulationparameters, etc. for HE preamble (or HEW preamble) decoding at an HE STA(or HEW STA). The set of parameters included in the HEW SIG-A field mayinclude one or more of Very High Throughput (VHT) PPDU modulationparameters transmitted by IEEE 802.11ac stations, as listed in Table IIbelow, to ensure backward compatibility with legacy STAs (e.g., IEEE802.11ac stations).

TABLE II Two parts of Number VHT-SIG-A Bit Field of bits DescriptionVHT-SIG-A1 B0-B1 BW 2 Set to 0 for 20 MHz, 1 for 40 MHz, 2 for 80 MHz,and 3 for 160 MHz and 80 + 80 MHz B2 Reserved 1 Reserved. Set to 1. B3STBC 1 For a VHT SU PPDU:  Set to 1 if space time block coding is usedand set to 0  otherwise. For a VHT MU PPDU:  Set to 0. B4-B9 Group ID 6Set to the value of the TXVECTOR parameter GROUP_ID. A value of 0 or 63indicates a VHT SU PPDU; otherwise, indicates a VHT MU PPDU. B10-B21NSTS/Partial 12 For a VHT MU PPDU: NSTS is divided into 4 user AIDpositions of 3 bits each. User position p, where 0 ≤ p ≤ 3, uses bitsB(10 + 3p) to B(12 + 3p). The number of space- time streams for user uare indicated at user position p = USER_POSITION[u] where u = 0, 1, . .. , NUM_USERS − 1 and the notation A[b] denotes the value of array A atindex b. Zero space-time streams are indicated at positions not listedin the USER_POSITION array. Each user position is set as follows:  Setto 0 for 0 space-time streams  Set to 1 for 1 space-time stream  Set to2 for 2 space-time streams  Set to 3 for 3 space-time streams  Set to 4for 4 space-time streams  Values 5-7 are reserved For a VHT SU PPDU:B10-B12  Set to 0 for 1 space-time stream  Set to 1 for 2 space-timestreams  Set to 2 for 3 space-time streams  Set to 3 for 4 space-timestreams  Set to 4 for 5 space-time streams  Set to 5 for 6 space-timestreams  Set to 6 for 7 space-time streams  Set to 7 for 8 space-timestreams B13-B21  Partial AID: Set to the value of the TXVECTOR parameter PARTIAL_AID. Partial AID provides an  abbreviated indicationof the intended recipient(s) of the  PSDU (see 9, 7a). B22TXOP_PS_NOT_ALLOWED 1 Set to 0 by VHT AP if it allows non-AP VHT STAs inTXOP power save mode to enter Doze state during a TXOP. Set to 1otherwise. The bit is reserved and set to 1 in VHT PPDUs transmitted bya non-AP VHT STA. B23 Reserved 1 Set to 1 VHT-SIG-A2 B0 Short GI 1 Setto 0 if short guard interval is not used in the Data field. Set to 1 ifshort guard interval is used in the Data field. B1 Short GI 1 Set to 1if short guard interval is used and N_(SYM) mod 10 = 9; N_(SYM)otherwise, set to 0. N_(SYM) is defined in 22.4.3. Disambiguation B2SU/MU[0] 1 For a VHT SU PPDU, B2 is set to 0 for BCC, 1 for LDPC CodingFor a VHT MU PPDU, if the MU[0] NSTS field is nonzero, then B2 indicatesthe coding used for user u with USER_POSITION[u] = 0; set to 0 for BCCand 1 for LDPC. If the MU[0] NSTS field is 0, then this field isreserved and set to 1. B3 LDPC Extra 1 Set to 1 if the LDPC PPDUencoding process (if an SU OFDM PPDU), or at least one LDPC user's PPDUencoding process Symbol (if a VHT MU PPDU), results in an extra OFDMsymbol (or symbols) as described in 22.3.10.5.4 and 22.3.10.5.5. Set to0 otherwise. B4-B7 SU VHT- 4 For a VHT SU PPDU: MCS/MU[1-3]  VHT-MCSindex Coding For a VHT MU PPDU:  If the MU[1] NSTS field is nonzero,then B4 indicates  coding for user u with USER_POSITION[u] = 1: set to 0 for BCC, 1 for LDPC. If the MU[1] NSTS field is 0, then  B4 is reservedand set to 1.  If the MU[2] NSTS field is nonzero, then B5 indicates coding for user u with USER_POSITION[u] = 2: set to 0  for BCC, 1 forLDPC. If the MU[2] NSTS field is 0, then  B5 is reserved and set to 1. If the MU[3] NSTS field is nonzero, then B6 indicates  coding for useru with USER_POSITION[u] = 3: set to 0  for BCC, 1 for LDPC. If the MU[3]NSTS field is 0, then  B6 is reserved and set to 1.  B7 is reserved andset to 1 B8 Beamformed 1 For a VHT SU PPDU:  Set to 1 if a Beamformingsteering matrix is applied to the  waveform in an SU transmission asdescribed in  20.3.11.11.2, set to 0 otherwise. For a VHT MU PPDU: Reserved and set to 1 NOTE-If equal to 1 smoothing is not recommended.B9 Reserved 1 Reserved and set to 1 B10-B17 CRC 8 CRC calculated as in20.3.9.4.4 with c7 in B10. Bits 0-23 of HT-SIG1 and bits 0-9 of HT-SIG2are replaced by bits 0-23 of VHT-SIG-A1 and bits 0-9 of VHT-SIG-A2,respectively. B18-B23: Tail 6 Used to terminate the trellis of theconvolutional decoder. Set to 0.

Table II illustrates fields, bit positions, numbers of bits, anddescriptions included in each of two parts, VHT-SIG-A1 and VHT-SIG-A2,of the VHT-SIG-A field defined by the IEEE 802.11ac standard. Forexample, a BW (BandWidth) field occupies two Least Significant Bits(LSBs), B0 and B1 of the VHT-SIG-A1 field and has a size of 2 bits. Ifthe 2 bits are set to 0, 1, 2, or 3, the BW field indicates 20 MHz, 40MHz, 80 MHz, or 160 and 80+80 MHz. For details of the fields included inthe VHT-SIG-A field, refer to the IEEE 802.11 ac-2013 technicalspecification, which is hereby incorporated by reference. In the HE PPDUframe format of the present disclosure, the HE-SIG-A field may includeone or more of the fields included in the VHT-SIG-A field, and it mayprovide backward compatibility with IEEE 802.11ac stations.

FIG. 9 depicts subchannel allocation in the HE PPDU frame formataccording to the present disclosure.

In FIG. 9, it is assumed that information indicating subchannelsallocated to STAs in HE PPDU indicates that 0 MHz subchannel isallocated to STA1 (i.e., no subchannel is allocated), a 5-MHz subchannelis allocated to each of STA2 and STA3, and a 10-MHz subchannel isallocated to STA4.

In the example of FIG. 9, an L-STF, an L-LTF, an L-SIG, and an HE-SIG-Amay be transmitted per channel (e.g., 20 MHz), an HE-STF and an HE-LTFmay be transmitted on each basic subchannel unit (e.g., 5 MHz), and anHE-SIG-B and a PSDU may be transmitted on each of the subchannelsallocated to STAs. A subchannel allocated to a STA has a size requiredfor PSDU transmission to the STA. The size of the subchannel allocatedto the STA may be an N (N=1, 2, 3, . . . ) multiple of the size of thebasic subchannel unit (i.e., a minimum-size subchannel unit). In theexample of FIG. 9, the size of a subchannel allocated to STA2 is equalto that of the basic subchannel unit, the size of a subchannel allocatedto STA3 is equal to that of the basic subchannel unit, and the size of asubchannel allocated to STA4 is twice the size of the basic subchannelunit.

FIG. 9 illustrates a plurality of HE-LTF elements and a plurality ofHE-LTF subelements which are distinguished in the time and frequencydomains. One HE-LTF element may correspond to one OFDM symbol in thetime domain and one subchannel unit (i.e., the bandwidth of a subchannelallocated to a STA) in the frequency domain. One HE-LTF subelement maycorrespond to one OFDM symbol in the time domain and one basicsubchannel unit (e.g. 5 MHz) in the frequency domain. In the example ofFIG. 9, one HE-LTF element includes one HE-LTF subelement in the 5-MHzsubchannel allocated to STA2 or STA3. On the other hand, one HE-LTFelement includes two HE-LTF subelements in the third subchannel (i.e.,10-MHz subchannel, allocated to STA4). An HE-LTF element and an HE-LTFsubelement are logical units and the PHY layer does not always operatein units of an HE-LTF element or HE-LTF subelement.

An HE-LTF symbol may correspond to a set of HE-LTF elements in one OFDMsymbol in the time domain and one channel unit (e.g. 20 MHz) in thefrequency domain. That is, one HE-LTF symbol may be divided into HE-LTFelements by a subchannel width allocated to a STA and into HE-LTFsubelements by the width of the basic subchannel unit in the frequencydomain.

An HE-LTF section may correspond to a set of HE-LTF elements in one ormore OFDM symbols in the time domain and one subchannel unit (i.e. thebandwidth of a subchannel allocated to a STA) in the frequency domain.An HE-LTF subsection may correspond to a set of HE-LTF elements in oneor more OFDM symbols in the time domain and one basic subchannel unit(e.g., 5 MHz) in the frequency domain. In the example of FIG. 9, oneHE-LTF section includes one HE-LTF subsection in the 5-MHz subchannelallocated to STA2 or STA3. On the other hand, one HE-LTF sectionincludes two HE-LTF subsections in the third subchannel (i.e., 10-MHzsubchannel, allocated to STA4).

An HE-LTF field may correspond to a set of HE-LTF elements (orsubelements), HE-LTF symbols, or HE-LTF sections (or subsections) for aplurality of STAs.

For the afore-described HE PPDU transmission, subchannels allocated to aplurality of HE STAs may be contiguous in the frequency domain. In otherwords, for HE PPDU transmission, the subchannels allocated to the HESTAs may be sequential and any intermediate one of the subchannels ofone channel (e.g., 20 MHz) may not be allowed to be unallocated orempty. Referring to FIG. 8, if one channel includes four subchannels, itmay not be allowed to keep the third subchannel unallocated and empty,while the first, second, and fourth subchannels are allocated to STAs.However, the present disclosure does not exclude non-allocation of anintermediate subchannel of one channel to a STA.

FIG. 10 depicts a subchannel allocation method according to the presentdisclosure.

In the example of FIG. 10, a plurality of contiguous channels (e.g.,20-MHz-bandwidth channels) and boundaries of the plurality of contiguouschannels are shown. In FIG. 10, a preamble may correspond to an L-STF,an L-LTF, an L-SIG, and an HE-SIG-A as illustrated in the examples ofFIGS. 8 and 9.

A subchannel for each HE STA may be allocated within one channel, andmay not be allocated with partially overlapping between a plurality ofchannels. That is, if there are two contiguous 20-MHz channels CH1 andCH2, subchannels for STAs paired for MU-MIMO-mode or OFDMA-modetransmission may be allocated either within CH1 or within CH2, and itmay be prohibited that one part of a subchannel exists in CH1 andanother part of the subchannel exists in CH2. This means that onesubchannel may not be allocated with crossing a channel boundary. Fromthe perspective of RUs supporting the MU-MIMO or OFDMA mode, a bandwidthof 20 MHz may be divided into one or more RUs, and a bandwidth of 40 MHzmay be divided into one or more RUs in each of two contiguous 20-MHzbandwidths, and no RU is allocated with crossing the boundary betweentwo contiguous 20-MHz bandwidths.

As described above, it is not allowed that one subchannel belongs to twoor more 20-MHz channels. Particularly, a 2.4-GHz OFDMA mode may supporta 20-MHz OFDMA mode and a 40-MHz OFDMA mode. In the 2.4-GHz OFDMA mode,it may not be allowed that one subchannel belongs to two or more 20-MHzchannels.

FIG. 10 is based on the assumption that subchannels each having the sizeof a basic subchannel unit (e.g., 5 MHz) in CH1 and CH2 are allocated toSTA1 to STA7, and subchannels, each having double the size (e.g., 10MHz) of the basic subchannel unit in CH4 and CH5, are allocated to STA8,STA9, and STA10.

As illustrated in the lower part of FIG. 10, although a subchannelallocated to STA1, STA2, STA3, STA5, STA6, or STA7 is fully overlappedonly with one channel (i.e., without crossing the channel boundary, orbelonging only to one channel), a subchannel allocated to STA4 ispartially overlapped with the two channels (i.e., crossing the channelboundary, or belonging to two channels). In the foregoing example of thepresent disclosure, the subchannel allocation to STA4 is not allowed.

As illustrated in the upper part of FIG. 10, although a subchannelallocated to STA8 or STA10 is fully overlapped only with one channel(i.e., without crossing the channel boundary, or belonging only to onechannel), a subchannel allocated to STA9 is partially overlapped withtwo channels (i.e., crossing the channel boundary, or belonging to twochannels). In the foregoing example of the present disclosure, thesubchannel allocation to STA9 is not allowed.

On the other hand, in some embodiments, it may be allowed to allocate asubchannel partially overlapped between a plurality of channels (i.e.,crossing the channel boundary, or belonging to two or more channels).For example, in SU-MIMO mode transmission, a plurality of contiguouschannels may be allocated to a STA and any of one or more subchannelsallocated to the STA may cross the boundary between two contiguouschannels.

While the following description is given with an assumption that onesubchannel has a channel bandwidth of 5 MHz in one channel having achannel bandwidth of 20 MHz, this is provided to simplify thedescription of the principle of the present disclosure and thus shouldnot be construed as limiting the present disclosure. For example, thebandwidths of a channel and a subchannel may be defined or allocated asvalues other than the above examples. In addition, a plurality ofsubchannels in one channel may have the same or different channelwidths.

FIG. 11 depicts the starting and ending points of an HE-LTF field in theHE PPDU frame format according to the present disclosure.

To support the MU-MIMO mode and the OFDMA mode, the HE PPDU frame formataccording to the present disclosure may include, in the HE-SIG-A field,information about the number of spatial streams to be transmitted to anHE STA allocated to each subchannel.

If MU-MIMO-mode or OFDMA-mode transmission is performed to a pluralityof HE STAs on one subchannel, the number of spatial streams to betransmitted to each of the HE STAs may be provided in the HE-SIG-A orHE-SIG-B field, which will be described later in additional detail.

FIG. 11 is based on the assumption that a first 5-MHz subchannel isallocated to STA1 and STA2 and two spatial streams are transmitted toeach STA in a DL MU-MIMO or OFDMA mode (i.e., a total of four spatialstreams are transmitted on one subchannel). For this purpose, an HE-STF,an HE-LTF, an HE-LTF, an HE-LTF, an HE-LTF, and an HE-SIG-B follow theHE-SIG-A field on the subchannel. The HE-STF is used for frequencyoffset estimation and phase offset estimation for the 5-MHz subchannel.The HE-LTFs are used for channel estimation for the 5-MHz subchannel.Since the subchannel carries four spatial streams, as many HE-LTFs(i.e., HE-LTF symbols or HE-LTF elements in an HE-LTF section) as thenumber of the spatial streams, that is, four HE-LTFs are transmitted tosupport MU-MIMO transmission.

According to an example of the present disclosure, the relationshipbetween a total number of spatial streams transmitted on one subchanneland a number of HE-LTFs is listed in Table III.

TABLE III Total number of spatial streams transmitted on one subchannelNumber of HE-LTFs 1 1 2 2 3 4 4 4 5 6 6 6 7 8 8 8

Referring to Table III as an example, if one spatial stream istransmitted on one subchannel, at least one HE-LTF needs to betransmitted on the subchannel. If an even number of spatial streams aretransmitted on one subchannel, at least as many HE-LTFs as the number ofthe spatial streams need to be transmitted. If an odd number of spatialstreams greater than one are transmitted on one subchannel, at least asmany HE-LTFs as a number that is 1 larger than the number of the spatialstreams need to be transmitted.

Referring to FIG. 11 again, it is assumed that the second 5-MHzsubchannel is allocated to STA3 and STA4 and one spatial stream per STAis transmitted in the DL MU-MIMO or OFDMA mode (i.e., a total of twospatial streams are transmitted on one subchannel). In this case, twoHE-LTFs need to be transmitted on the second subchannel, however, in theexample of FIG. 11, an HE-STF, an HE-LTF, an HE-LTF, an HE-LTF, anHE-LTF, and an HE-SIG-B follow the HE-SIG-A field on the subchannel(i.e., four HE-LTFs are transmitted). This is for the purpose of settingthe same starting time of PSDU transmission for subchannels allocated toother STAs paired with STA3 and STA4 for MU-MIMO transmission. If onlytwo HE-LTFs are transmitted on the second subchannel, PSDUs aretransmitted at different time points on the first and secondsubchannels. PSDU transmission on each subchannel at a different timepoint results in discrepancy between OFDM symbol timings of subchannels,thereby disrupting orthogonality (i.e., orthogonality is notmaintained). To overcome this problem, an additional constraint needs tobe imposed for HE-LTF transmission.

Basically, transmission of as many HE-LTFs as required is sufficient inan SU-MIMO or non-OFDMA mode. However, timing synchronization (oralignment) with fields transmitted on subchannels for other paired STAsis required in the MU-MIMO or OFDMA mode. Accordingly, the number ofHE-LTFs may be determined for all other subchannels based on asubchannel having the maximum number of streams in MU-MIMO-mode orOFDMA-mode transmission.

Specifically, the numbers of HE-LTFs may be determined for allsubchannels according to the maximum of the number of HE-LTFs (HE-LTFsymbols or HE-LTF elements in an HE-LTF section) required according tothe total number of spatial streams transmitted on each subchannel, fora set of HE STAs allocated to each subchannel. A “set of HE STAsallocated to each subchannel” is one HE STA in the SU-MIMO mode, and aset of HE STAs paired across a plurality of subchannels in the MU-MIMOmode. The ‘number of spatial streams transmitted on each subchannel’ isthe number of spatial streams transmitted to one HE STA in the SU-MIMOmode, and the number of spatial streams transmitted to a plurality of HESTAs paired on the subchannel in the MU-MIMO mode.

That is, it may be said that an HE-LTF field starts at the same timepoint and ends at the same time point in an HE PPDU for all users (i.e.HE STAs) in MU-MIMO-mode or OFDMA-mode transmission. Or it may be saidthat the lengths of HE-LTF sections are equal on a plurality ofsubchannels for all users (i.e. HE STAs) in MU-MIMO-mode or OFDMA-modetransmission. Or it may be said that the number of HE-LTF elementsincluded in each HE-LTF section is equal on a plurality of subchannelsfor all users (i.e. HE STAs) in MU-MIMO-mode or OFDMA-mode transmission.Accordingly, PSDU transmission timings may be synchronized among aplurality of subchannels for all HE STAs in MU-MIMO-mode or OFDMA-modetransmission.

As described above, the number of HE-LTF symbols (refer to FIG. 8) maybe 1, 2, 4, 6, or 8 in HE PPDU transmission in the MU-MIMO or OFDMAmode, determined according to the maximum of the numbers of spatialstreams on each of a plurality of subchannels. A different number ofspatial streams may be allocated to each of a plurality of subchannels,and the number of spatial streams allocated to one subchannel is thenumber of total spatial streams for all users allocated to thesubchannel. That is, the number of HE-LTF symbols may be determinedaccording to the number of spatial streams allocated to a subchannelhaving a maximum number of spatial streams by comparing the number oftotal spatial streams for all users allocated to one of a plurality ofsubchannels with the number of total spatial streams for all usersallocated to another subchannel.

Specifically, in HE PPDU transmission in the OFDMA mode, the number ofHE-LTF symbols may be 1, 2, 4, 6, or 8, determined based on the numberof spatial streams transmitted in a subchannel having a maximum numberof spatial streams across a plurality of subchannels. Further, in HEPPDU transmission in the OFDMA mode, the number of HE-LTF symbols may bedetermined based on whether the number of spatial streams transmitted ina subchannel having a maximum number of spatial streams across aplurality of subchannels is odd or even (refer to Table III). That is,in HE PPDU transmission in the OFDMA mode, when the number (e.g., K) ofspatial streams transmitted in a subchannel having a maximum number ofspatial streams across a plurality of subchannels is an even number, thenumber of HE-LTF symbols may be equal to K. In HE PPDU transmission inthe OFDMA mode, when the number, K, of spatial streams transmitted in asubchannel having a maximum number of spatial streams across a pluralityof subchannels is an odd number greater than one, the number of HE-LTFsymbols may be equal to K+1.

When only one STA is allocated to one subchannel in OFDMA mode (i.e.,OFDMA mode without using MU-MIMO), a subchannel having a maximum numberof spatial streams across a plurality of subchannels may be determinedby the number of spatial streams for a STA allocated to each subchannel.When more than one STA is allocated to one subchannel in OFDMA mode(i.e., OFDMA mode using MU-MIMO), a subchannel having a maximum numberof spatial streams across a plurality of subchannels may be determinedby the number of STAs allocated to each subchannel and the number ofspatial streams for each STA allocated to each subchannel (e.g., if STA1and STA2 are allocated to one subchannel, sum of the number of spatialstreams for STA1 and the number of spatial streams for STA2).

When transmitting an HE PPDU frame in the MU-MIMO or OFDMA mode, atransmitter may generate P (where P is an integer equal to or largerthan 1) HE-LTF symbols (refer to FIG. 8) and transmit an HE PPDU frameincluding at least the P HE-LTF symbols and a Data field to a receiver.The HE PPDU frame may be divided into Q subchannels in the frequencydomain (Q is an integer equal to or larger than 2). Each of the P HE-LTFsymbols may be divided into Q HE-LTF elements corresponding to the Qsubchannels in the frequency domain. That is, the HE PPDU may include PHE-LTF elements on one subchannel (herein, the P HE-LTF elements maybelong to one HE-LTF section on the subchannel).

As described above, the number of HE-LTF elements (i.e., P) in one ofthe Q subchannels may be equal to the number of HE-LTF elements (i.e.,P) of another subchannel. Also, the number of HE-LTF elements (i.e., P)included in an HE-LTF section in one of the Q subchannels may be equalto the number of HE-LTF elements (i.e., P) included in an HE-LTF sectionin another subchannel. The HE-LTF section of one of the Q subchannelsmay start and end at the same time points as the HE-LTF section ofanother subchannel. Also, the HE-LTF sections may start and end at thesame time points across the Q subchannels (i.e., across all users orSTAs).

Referring to FIG. 11 again, the third 5-MHz subchannel is allocated toSTA5 and one spatial stream is transmitted on the subchannel in SU-MIMO(considering all subchannels, a plurality of spatial streams aretransmitted to STA1 to STA6 in MU-MIMO or OFDMA mode). In this case,although transmission of one HE-LTF is sufficient for the subchannel, asmany HE-LTFs as the maximum of the numbers of HE-LTFs on the othersubchannels, that is, four HE-LTFs are transmitted on the subchannel inorder to align the starting points and ending points of the HE-LTFfields of the subchannels.

The fourth 5-MHz subchannel is allocated to STA6 and one spatial streamis transmitted on the subchannel in SU-MIMO (considering all othersubchannels, a plurality of spatial streams are transmitted to STA1 toSTA6 in MU-MIMO or OFDMA mode). In this case, although transmission ofone HE-LTF is sufficient for the subchannel, as many HE-LTFs as themaximum of the numbers of HE-LTFs on the other subchannels, that is,four HE-LTFs are transmitted on the subchannel in order to align thestarting points and ending points of the HE-LTF fields of thesubchannels.

In the example of FIG. 11, the remaining two HE-LTFs except two HE-LTFsrequired for channel estimation of STA3 and STA4 on the secondsubchannel, the remaining three HE-LTFs except one HE-LTF required forchannel estimation of STA5 on the third subchannel, and the remainingthree HE-LTFs except one HE-LTF required for channel estimation of STA6on the fourth subchannel may be said to be placeholders that are notactually used for channel estimation at the STAs.

FIG. 12 depicts an HE-SIG-B field and an HE-SIG-C field in the HE PPDUframe format according to the present disclosure.

To effectively support MU-MIMO-mode or OFDMA-mode transmission in the HEPPDU frame format according to the present disclosure, independentsignaling information may be transmitted on each subchannel.Specifically, a different number of spatial streams may be transmittedto each of a plurality of HE STAs that receive an MU-MIMO-mode orOFDMA-mode transmission simultaneously. Therefore, information about thenumber of spatial streams to be transmitted should be indicated to eachHE STA.

Information about the number of spatial streams on one channel may beincluded in, for example, an HE-SIG-A field. An HE-SIG-B field mayinclude spatial stream allocation information about one subchannel.Also, an HE-SIG-C field may be transmitted after transmission ofHE-LTFs, including Modulation and Coding Scheme (MCS) information abouta PSDU and information about the length of the PSDU, etc.

FIG. 13 depicts OFDM symbol durations and GI lengths in the HE PPDUframe format according to the present disclosure.

In the HE PPDU frame format according to the present disclosure, L-STF,L-LTF, L-SIG, and HE-SIG-A fields may be configured with 4.0 μs OFDMsymbols based on 64-FFT. One OFDM symbol has a GI of 0.8 μs. In thepresent disclosure, a GI value applied to the L-STF, L-LTF, L-SIG, andHE-SIG-A fields is defined as G1. The L-STF, L-LTF, L-SIG, and HE-SIG-Afields may include 3.2-μs OFDM symbols based on 64-FFT, excluding theGIs. The term 64 FFT-based symbol is used mainly based on a channelbandwidth of 20 MHz. If the term 64 FFT-based symbol is usedirrespective of a channel bandwidth, a 64 FFT-based symbol may mean asymbol having a symbol duration of 3.2 μs and a subcarrier spacing of312.5 kHz.

The following HE-STF, HE-LTF, HE-SIG-B, and PSDU fields may include16-μs OFDM symbols based on 256-FFT. The OFDM symbol duration may bechanged according to a GI value. Two types of GI values may be definedfor one OFDM symbol during different time periods. A GI value applied tothe OFDM symbols of the HE-STF, HE-LTF, and HE-SIG-B fields is definedas G2 and a GI value applied to the OFDM symbols of the PSDU is definedas G3. Excluding the GIs, the HE-STF, HE-LTF, HE-SIG-B, and PSDU fieldsmay be configured with 12.8-μs OFDM symbols based on 256-FFT. The term256 FFT-based symbol is used mainly based on a channel bandwidth of 20MHz. If the term 256 FFT-based symbol is used irrespective of a channelbandwidth, a 256 FFT-based symbol may mean a symbol having a symbolduration of 12.8 μs and a subcarrier spacing of 78.125 kHz.

The values of G2 and G3 may be equal or different. If G2 and G3 areequal, G2 and G3 may be defined as one parameter without distinguishingbetween G2 and G3. In one embodiment, unlike GI, G2 and G3 may varyaccording to a transmitted PPDU transmission vector, rather than beingfixed values (i.e., predetermined values). This is because the lengthsof the HE-STF, HE-LTF, and HE-SIG-B fields to which G2 is applied mayvary according to a PPDU transmission vector and the length of the PSDUto which G3 is applied may also vary according to the PPDU transmissionvector.

For example, G1 may have a fixed value (i.e., a predetermined value) of0.8 μs, G2 may be a value selected from 3.2 μs, 1.6 μs, 0.8 μs, and 0.4μs, and G3 may be a value selected from among 3.2 μs, 1.6 μs, 0.8 μs,and 0.4 μs. Also, G1 may have a fixed value (i.e., a predeterminedvalue) of 0.8 μs, and G2 or G3 may be a value selected or determinedfrom among 3.2 μs, 1.6 μs, 0.8 μs, and 0.4 μs. In one embodiment, G1does not require separate signaling because G1 is a fixed value, andsignaling information indicating G2 and G3 may be provided to an HE STAin the HE-SIG-A field.

In one embodiment, G2 and G3 are applied commonly across all OFDMsymbols transmitted during a corresponding time period and across allsubchannels. Accordingly, PSDU transmission timings and OFDM symboltimings may be synchronized. For example, it may not be allowed to applya 3.2-μs G2 value to a subchannel and a 1.6-μs or 0.8-μs G2 value toanother subchannel during a specific time period. Rather, the same3.2-μs G2 value may be applied to the subchannels during the same timeperiod. In a similar example, it may not be allowed to apply a 1.6-μs G3value to a subchannel and a 3.2-μs or 0.8-μs G3 value to anothersubchannel during a specific time period. Rather, the same 1.6-μs G3value may be applied to the subchannels during the same time period.

In the case where an HE PPDU frame format having HE-LTF sections ofdifferent lengths for subchannels is used (i.e., in the case where thenumber of HE-LTFs is not determined for each subchannel based on themaximum of the number of HE-LTFs required according to the total numberof spatial streams transmitted on each subchannel in a set of HE STAsallocated to each of subchannels, as described in the example of FIG.11), if the values of G2 and G3 are different, PSDUs are transmitted ondifferent subchannels at different time points and OFDM symbol timingsare not synchronized. Therefore, values of G2 and G3 may need to beselected or determined as a same value.

In the case where an HE PPDU frame format having HE-LTF sections of thesame length for subchannels is used (i.e., in the case where the numberof HE-LTFs is determined for each subchannel based on the maximum of thenumbers of HE-LTFs required according to the total number of spatialstreams transmitted on each subchannel in a set of HE STAs allocated toeach of subchannels, as described in the example of FIG. 11), eventhough the values of G2 and G3 are different, PSDUs are transmitted onthe subchannels at the same time point, without causing discrepancybetween OFDM symbol timings. Therefore, values of G2 and G3 may beselected or determined as different values. However, even in this case,the present disclosure does not exclude that values of G2 and G3 may beselected or determined as a same value.

In the example of FIG. 13, OFDM symbol durations S1, S2, and S3 may beapplied respectively to time periods to which the GIs G1, G2, and G3 areapplied.

FIG. 14 depicts an example HE PPDU frame format for a wide channel bandaccording to the present disclosure.

Referring to FIG. 14, the HE PPDU frame format for one 20-MHz channelillustrated in the example of FIG. 13 is extended to two 20-MHzchannels. Similarly, HE PPDU frame formats for the channel bandwidths of80 MHz and 160 MHz may be configured by extending the HE PPDU frameformat for one 20-MHz channel illustrated in the example of FIG. 13 tofour and eight 20-MHz channels, respectively.

There is no modification involved in extending the HE PPDU frame formatfor one 20-MHz channel. In other words, all subchannels across one ormore 20-MHz channels are the same in terms of PSDU transmission timepoints, OFDM symbol durations, and GIs.

From this viewpoint, the example described with reference to FIG. 11 inwhich “the lengths of HE-LTF sections across subchannels are equal” maybe extended to simultaneous application on a channel basis as well as ona subchannel basis. Therefore, PSDU transmission timings and OFDM symboltimings are synchronized for users paired for MU-MIMO-mode or OFDMA-modetransmission, thus maintaining orthogonality. This channel-based examplewill be described below.

Basically in SU-MIMO-mode or non-OFDMA-mode transmission, it issufficient to transmit as many HE-LTFs as required. However, the timingsof fields transmitted on subchannels for other paired STAs need to besynchronized (or aligned) across all subchannels over one or more 20-MHzchannels in MU-MIMO-mode or OFDMA-mode transmission. Therefore, thenumbers of HE-LTFs on all other subchannels over one or more 20-MHzchannels may be determined based on a subchannel having a maximum numberof streams among all subchannels over one or more 20-MHz channels inMU-MIMO-mode or OFDMA-mode transmission.

Specifically, the number of HE-LTFs to be transmitted on all subchannelsmay be determined according to the maximum of the number of HE-LTFsrequired according to the total numbers of spatial streams transmittedon each subchannel over one or more 20-MHz channels, for a set of HESTAs allocated to each of the subchannels. Herein, ‘the set of HE STAsallocated to each of the subchannels over one or more 20-MHz channels’is one HE STA in the SU-MIMO mode, whereas it is a set of a plurality ofHE STAs paired on all subchannels over one or more 20-MHz channels inthe MU-MIMO mode or OFDMA mode. The ‘total number of spatial streamstransmitted on each of all subchannels over one or more 20-MHz channels’is the number of spatial streams transmitted to one HE STA in theSU-MIMO mode and the number of spatial streams transmitted to aplurality of HE STAs paired on the subchannel in the MU-MIMO mode orOFDMA mode.

That is, it may be said that an HE-LTF field starts at the same timepoint and ends at the same time point on all subchannels over one ormore 20-MHz channels for all users (i.e., HE STAs) in MU-MIMO-mode orOFDMA-mode transmission of an HE PPDU. Or it may be said that thelengths of HE-LTF sections are equal on all subchannels over one or more20-MHz channels for all HE STAs in MU-MIMO-mode or OFDMA-modetransmission. Or it may be said that the number of HE-LTF elementsincluded in each HE-LTF section is equal in all subchannels over one ormore 20-MHz channels for all HE STAs in MU-MIMO-mode or OFDMA-modetransmission. Accordingly, PSDU transmission timings may be synchronizedbetween all subchannels over one or more 20-MHz channels for all HE STAsin MU-MIMO-mode or OFDMA-mode transmission.

In FIG. 14, the OFDM symbol duration and GI of L-STF, L-LTF, L-SIG, andHE-SIG-A fields on the first 20-MHz channel are S1 and G1, respectively.Like the first 20-MHz channel, the second 20-MHz channel has S1 and G1respectively as the OFDM symbol duration and GI of L-STF, L-LTF, L-SIG,and HE-SIG-A fields.

In FIG. 14, the OFDM symbol duration and GI of an HE-STF field, aplurality of HE-LTFs, and an HE-SIG-B field on the first 20-MHz channelare S2 and G2, respectively. Like the first 20-MHz channel, the OFDMsymbol duration and GI of an HE-STF field, a plurality of HE-LTFs, andan HE-SIG-B field on the second 20-MHz channel are also S2 and G2,respectively.

In FIG. 14, the OFDM symbol duration and GI of a PSDU on the first20-MHz channel are S3 and G3, respectively. Like the first 20-MHzchannel, the OFDM symbol duration and GI of a PSDU on the second 20-MHzchannel are also S3 and G3, respectively.

This example it is shown that if the OFDM symbol duration and GI of one20-MHz channel are determined based on 64-FFT, the OFDM symbol durationand GI of the other 20-MHz channel(s) should be determined based on64-FFT. In other words, if the OFDM symbol duration and GI of one 20-MHzchannel are determined based on 64-FFT, the OFDM symbol duration and GIof the other 20-MHz channel(s) should not be determined based on256-FFT.

In a modified example, although subchannels within one 20-MHz channelmay have the same OFDM symbol durations and the same GIs, subchannelswithin another 20-MHz channel may have different OFDM symbol durationsand GIs. For example, while S2, G2, S3, and G3 are applied as OFDMsymbol durations and GIs for subchannels within the first 20-MHzchannel, different values (e.g., S4, G4, S5, and G5) may be applied asOFDM symbol durations and GIs for subchannels within the second 20-MHzchannel. Even in this case, the OFDM symbol duration and GI, S1 and G1,applied to L-STF, L-LTF, and L-SIG fields in a different 20-MHz channelmay be the same fixed values in every 20-MHz channel.

Further, this modified example may include application of the exampledescribed before with reference to FIG. 11 in which ‘subchannels havethe same HE-LTF section length’ only to subchannels within one 20-MHzchannel, not to the HE-LTF section length of subchannels in another20-MHz channel.

With reference to the foregoing examples of the present disclosure,mainly the features of an HE PPDU frame structure applicable to a DLMU-MIMO-mode or OFDMA-mode transmission that an AP transmitssimultaneously to a plurality of STAs has been described. Now, adescription will be given of the features of an HE PPDU frame structureapplicable to a UL MU-MIMO-mode or OFDMA-mode transmission that aplurality of STAs transmit simultaneously to an AP.

The above-described various examples of structures of the HE PPDU frameformat supporting MU-MIMO-mode or OFDMA-mode transmission should not beunderstood as applicable only to DL without being applicable to UL.Rather, the examples should be understood as also applicable to UL. Forexample, the above-described example HE PPDU frame formats may also beused for a UL HE PPDU transmission that a plurality of STAssimultaneously transmit to a single AP.

However, in the case of a DL MU-MIMO-mode or OFDMA-mode HE PPDUtransmission that an AP simultaneously transmits to a plurality of STAs,the transmission entity, AP has knowledge of the number of spatialstreams transmitted to an HE STA allocated to each of a plurality ofsubchannels. Therefore, the AP may include, in an HE-SIG-A field or anHE-SIG-B field, information about the total number of spatial streamstransmitted across a channel, a maximum number of spatial streams (i.e.,information being a basis of the number of HE-LTF elements (or thestarting point and ending point of an HE-LTF section) on eachsubchannel), and the number of spatial streams transmitted on eachsubchannel. In contrast, in the case of a UL MU-MIMO-mode or OFDMA-modeHE PPDU transmission that a plurality of STAs simultaneously transmit toan AP, each STA being a transmission entity may only be aware of thenumber of spatial streams in an HE PSDU that it will transmit, withoutknowledge of the number of spatial streams in an HE PSDU transmitted byanother STA paired with the STA. Accordingly, the STA may determineneither the total number of spatial streams transmitted across a channelnor a maximum number of spatial streams.

To solve this problem, a common parameter (i.e., a parameter appliedcommonly to STAs) and an individual parameter (a separate parameterapplied to an individual STA) may be configured as follows in relationto a UL HE PPDU transmission.

For simultaneous UL HE PPDU transmissions from a plurality of STAs to anAP, a protocol may be designed in such a manner that the AP sets acommon parameter or individual parameters (common/individual parameters)for the STAs for the UL HE PPDU transmissions and each STA operatesaccording to the common/individual parameters. For example, the AP maytransmit a trigger frame (or polling frame) for a UL MU-MIMO-mode orOFDMA-mode transmission to a plurality of STAs. The trigger frame mayinclude a common parameter (e.g., the number of spatial streams across achannel or a maximum number of spatial streams) and individualparameters (e.g., the number of spatial streams allocated to eachsubchannel), for the UL MU-MIMO-mode or OFDMA-mode transmission. As aconsequence, an HE PPDU frame format applicable to a UL MU-MIMO or OFDMAmode may be configured without modification to an example HE PPDU frameformat applied to a DL MU-MIMO or OFDMA mode. For example, each STA mayconfigure an HE PPDU frame format by including information about thenumber of spatial streams across a channel in an HE-SIG-A field,determining the number of HE-LTF elements (or the starting point andending point of an HE-LTE section) on each subchannel according to themaximum number of spatial streams, and including information about thenumber of spatial streams for the individual STA in an HE-SIG-B field.

Alternatively, if the STAs operate according to the common/individualparameters received in the trigger frame from the AP, each STA does notneed to indicate the common/individual parameters to the AP during an HEPPDU transmission. Therefore, this information may not be included in anHE PPDU. For example, each STA may determine the total number of spatialstreams, the maximum number of spatial streams, and the number ofspatial streams allocated to individual STA, as indicated by the AP, andconfigure an HE PPDU according to the determined numbers, withoutincluding information about the total number of spatial streams or thenumber of spatial streams allocated to the STA in the HE PPDU.

On the other hand, if the AP does not provide common/individualparameters in a trigger frame, for a UL MIMO-mode or OFDMA-mode HE PPDUtransmission, the following operation may be performed.

Common transmission parameters (e.g., channel BandWidth (BW)information, etc.) for simultaneously transmitted HE PSDUs may beincluded in HE-SIG-A field, but parameters that may be different forindividual STAs (e.g., the number of spatial streams, an MCS, andwhether STBC is used or not, for each individual STA) may not beincluded in HE-SIG-A field. Although the individual parameters may beincluded in HE-SIG-B field, information about the number of spatialstreams and information indicating whether STBC is used or not, need tobe transmitted before an HE-LTF field because the number of spatialstreams and the information indicating whether STBC is used or not aresignificant to determination of configuration information about apreamble and a PSDU in an HE PPDU frame format (e.g., the number ofHE-LTF elements is determined according to a combination of the numberof spatial streams and the information indicating whether STBC is usedor not). For this purpose, an HE PPDU frame format as illustrated inFIG. 15 may be used for a UL HE PPDU transmission.

FIG. 15 depicts another example HE PPDU frame format according to thepresent disclosure. The HE PPDU frame format illustrated in FIG. 15 ischaracterized in that a structure of HE-SIG-A, HE-SIG-B, and HE-SIG-Cfields similar to that in FIG. 12 is used for a UL PPDU transmission.

As described before, if a UL MU-MIMO-mode or OFDMA-mode transmission isperformed by triggering of an AP (according to common/individualparameters provided by the AP), an individual STA may not need to reportan individual parameter to the AP. In this case, one or more of anHE-SIG-B field, an HE-SIG-C field, and a first HE-LTF element (i.e., anHE-LTF between an HE-STF field and an HE-SIG-B field) illustrated inFIG. 15 may not be present. In this case, a description of each fieldgiven below may be applicable only in the presence of the field.

In the example of FIG. 15, an HE-SIG-A field is transmitted per channel(i.e., per 20-MHz channel) and may include transmission parameterscommon to simultaneously transmitted HE PSDUs. Since the sameinformation is transmitted in the fields from the L-STF to HE-SIG-A inUL PPDUs transmitted by HE STAs allocated to subchannels, the AP mayreceive the same signals from the plurality of STAs successfully.

An HE-SIG-B field is transmitted per subchannel in one channel. TheHE-SIG-B field may have an independent parameter value according to thetransmission characteristics of an HE PSDU transmitted on eachsubchannel. The HE-SIG-B field may include spatial stream allocationinformation and information indicating whether STBC is used or not, foreach subchannel. If MU-MIMO is applied to a subchannel (i.e., if aplurality of STAs perform transmission on a subchannel), the HE-SIG-Bfield may include a common parameter for the plurality of STAs paired onthe subchannel.

An HE-SIG-C field is transmitted on the same subchannel as the HE-SIG-Bfield and may include information about an MCS and a packet length. IfMU-MIMO is applied to a subchannel (i.e., if a plurality of STAs performtransmission on a subchannel), the HE-SIG-C field may include respectiveindividual parameters for each of the plurality of STAs paired on thesubchannel.

Similar to DL MU-MIMO-mode or OFDMA-mode HE PPDU transmission, iftransmission of PSDUs start at different time points on subchannels inUL MU-MIMO-mode or OFDMA-mode HE PPDU transmission, and if OFDM symbolsare not aligned accordingly, then the implementation complexity of an APthat receives a plurality of PSDUs is increased. To solve this problem,‘the number of HE-LTFs may be determined for all subchannels accordingto the maximum of the numbers of HE LTFs required according to the totalnumbers of spatial streams transmitted on each subchannel for a set ofHE STAs allocated to each of subchannels’ as described with reference tothe example of FIG. 11.

This feature may mean that the HE-LTF field start at the same time pointand end at the same time point across all users (i.e., HE STAs) in ULMU-MIMO-mode or OFDMA-mode transmission. Or it may be said that theHE-LTF sections of a plurality of subchannels have the same lengthacross all HE STAs in UL MU-MIMO-mode or OFDMA-mode transmission. Or itmay be said that each of the HE-LTF sections of a plurality ofsubchannels includes the same number of HE-LTF elements across all HESTAs in UL MU-MIMO-mode or OFDMA-mode transmission. Therefore, PSDUtransmission timings are synchronized between a plurality of subchannelsacross all HE STAs in UL MU-MIMO-mode or OFDMA-mode transmission.

In the HE PPDU frame format supporting UL MIMO-mode or OFDMA-modetransmission illustrated in FIG. 15, the L-STF, L-LTF, L-SIG, andHE-SIG-A fields may include 4.0-μs OFDM symbols based on 64-FFT. OneOFDM symbol has a GI of 0.8 μs. In the present description, a GI valueapplied to the L-STF, L-LTF, L-SIG, and HE-SIG-A fields is defined asG1. Excluding the GI, the L-STF, L-LTF, L-SIG, and HE-SIG-A fields maybe configured as 3.2-μs OFDM symbols based on 64-FFT.

In the example of FIG. 15, an HE-STF field, an HE-LTF field, an HE-SIG-Bfield, HE-LTF elements(s) in an HE-LTF section, an HE-SIG-C field and aPSDU may include 16-μs OFDM symbols based on 256-FFT. The OFDM symbolduration may be changed according to a GI value. Two types of GI valuesmay be defined for one OFDM symbol for different time periods. A GIvalue applied to the OFDM symbols of the HE-STF field, the HE-LTF field,the HE-SIG-B field, the HE-LTF elements(s) in the HE-LTF section, andthe HE-SIG-C field is defined as G2 and a GI value applied to the OFDMsymbols of the PSDU is defined as G3. Excluding the GIs, the HE-STFfield, the HE-LTF field, the HE-SIG-B field, and the PSDU may include12.8-μs OFDM symbols based on 256-FFT.

The values of G2 and G3 may be equal or different. If G2 and G3 areequal, G2 and G3 may be defined as one parameter without distinguishingG2 from G3. In one embodiment, unlike G1, G2 and G3 may vary accordingto each transmitted PPDU transmission vector, rather than being fixedvalues (i.e. predetermined values known to both a transmitter and areceiver). This is because the lengths of the HE-STF, the HE-LTF, theHE-SIG-B, the HE-LTF element(s) in an HE-LTF section, and the HE-SIG-Cto which G2 is applied may vary according to a PPDU transmission vectorand the length of the PSDU to which G3 is applied may also varyaccording to the PPDU transmission vector.

In another example, the G1 applied to the L-STF, L-LTF, L-SIG, andHE-SIG-A fields (to which 64-FFT is applied) may be a fixed value (i.e.,a predefined value known to both a transmitter and a receiver) and oneof G2 and G3 (if G2 and G3 are equal, they may be defined as oneparameter) applied to the following fields (i.e., the HE-STF, HE-LTF,HE-SIG-B, HE-SIG-C, and PSDU to which 256-FFT is applied) may beconfigured or indicated as a variable value (e.g., one of 3.2 μs, 1.6μs, 0.8 μs, and 0.4 μs).

More specifically, G1 may have a fixed value (i.e. a predefined valueknown to both a transmitter and a receiver) of 0.8 μs, G2 may be a valueselected or indicated from among 3.2 μs, 1.6 μs, 0.8 μs, and 0.4 μs, andG3 may be a value selected or indicated from among 3.2 μs, 1.6 μs, 0.8μs, and 0.4 μs. Also, G1 may be a fixed value (i.e. a predefined valueknown to both a transmitter and a receiver) of 0.8 μs, and G2 or G3 maybe a value selected or indicated from among 3.2 μs, 1.6 μs, 0.8 μs, and0.4 μs. G1 does not require signaling because G1 is a fixed value, andsignaling information indicating G2 and G3 may be provided to the AP. Ifan HE STA performs UL transmission according to triggering of the AP (orbased on parameters provided by the AP), the HE-STA does not need toindicate the value of G2 or G3 to the AP.

G2 and G3 are applied commonly across all OFDM symbols transmittedduring a corresponding time period and across all subchannels.Accordingly, PSDU transmission timings may be synchronized, and OFDMsymbol timings may be synchronized. For example, it is not allowed thata 3.2-μs G2 value is applied to a subchannel during a specific timeperiod, while a 1.6-μs or 0.8-μs G2 value is applied to othersubchannels during the same time period. Rather, the same 3.2-μs G2value may be applied to other subchannels during the same time period.In a similar example, it is not allowed that a 1.6-μs G3 value isapplied to a subchannel during a specific time period, while a 3.2-μs or0.8-μs G3 value is applied to other subchannels during the same timeperiod. Rather, the same 1.6-μs G3 value may be applied to othersubchannels during the same time period.

In the case where an HE PPDU frame format having HE-LTF sections ofdifferent lengths for subchannels is used (i.e., in the case where ‘thenumber of HE-LTFs is not determined for each subchannel based on themaximum of the numbers of HE-LTFs required according to the totalnumbers of spatial streams transmitted on subchannels in a set of HESTAs allocated to each of the subchannels’), if the values of G2 and G3are different, a PSDU is transmitted on each subchannel at a differenttime point and OFDM symbol timings are not synchronized. Therefore, thesame values for G2 and G3 may need to be selected or indicated in thiscase.

In the case where an HE PPDU frame format having HE-LTF sections of thesame length for subchannels is used (i.e., in the case where ‘the numberof HE-LTFs is determined for each subchannel based on the maximum of thenumbers of HE-LTFs required according to the total numbers of spatialstreams transmitted on subchannels in a set of HE STAs allocated to eachof the subchannels’), even though the values of G2 and G3 are different,PSDUs are transmitted on the subchannels at the same time point, withoutcausing discrepancy between OFDM symbol timings. Therefore, selection orindication of different values for G2 and G3 does not cause a problem.However, even in this case, selection or indication of the same valuesfor G2 and G3 is not excluded.

In the example of FIG. 15, OFDM symbol durations S1, S2, and S3 may beapplied respectively to time periods to which the GIs G1, G2, and G3 areapplied.

As described before, a plurality of STAs may simultaneously transmitPSDUs in an HE PPDU frame format on their allocated subchannels or ontheir allocated spatial streams to an AP (i.e., referred to as ULMU-MIMO or OFDMA transmission or “UL MU transmission”) and maysimultaneously receive PSDUs in the HE PPDU frame format on theirallocated subchannels on their allocated spatial streams from the AP(i.e., referred to as DL MU-MIMO or OFDMA transmission or “DL MUtransmission”).

FIGS. 16 and 17 depict operating channels in a WLAN system.

Basically, the WLAN system may support a single channel having abandwidth of 20 MHz as a BSS operating channel. The WLAN system may alsosupport a BSS operating channel having a bandwidth of 40 MHz, 80 MHz, or160 MHz by bonding a plurality of contiguous 20-MHz channels (refer toFIG. 16). Further, the WLAN system may support a BSS operating channelhaving a bandwidth of 160 MHz including non-contiguous 80-MHz channels(called a bandwidth of 80+80 MHz) (refer to FIG. 17).

As illustrated in FIG. 16, one 40-MHz channel may include a primary20-MHz channel and a secondary 20-MHz channel which are contiguous. One80-MHz channel may include a primary 40-MHz channel and a secondary40-MHz channel which are contiguous. One 160-MHz channel may include aprimary 80-MHz channel and a secondary 80-MHz channel which arecontiguous. As illustrated in FIG. 17, one 80+80-MHz channel may includea primary 80-MHz channel and a secondary 80-MHz channel which arenon-contiguous.

A primary channel is defined as a common channel for all STAs within aBSS. The primary channel may be used for transmission of a basic signalsuch as a beacon. The primary channel may also be a basic channel usedfor transmission of a data unit (e.g., a PPDU). If a STA uses a channelwidth larger than the channel width of the primary channel, for datatransmission, the STA may use another channel within a correspondingchannel, in addition to the primary channel. This additional channel isreferred to as a secondary channel.

A STA according to an Enhanced Distributed Channel Access (EDCA) schememay determine a transmission bandwidth (or a transmission channel width)as follows.

Upon generation of a transmission frame, a STA (e.g., an AP or a non-APSTA) may perform a back-off procedure on a primary channel in order toacquire a Transmission Opportunity (TXOP). For this purpose, the STA maysense the primary channel during a DIFS or AIFS[i]. If the primarychannel is idle, the STA may attempt to transmit the frame. The STA mayselect a random back-off count, wait for a slot time corresponding tothe selected random back-off count, and then attempt to transmit theframe. The random back-off count may be determined to be a value rangingfrom 0 to CW (CW is a value of a contention window parameter).

When the random back-off procedure starts, the STA may activate aback-off timer according to the determined back-off count and decrementthe back-off count by 1 each time. If the medium of the correspondingchannel is monitored as busy, the STA discontinues the count-down andwaits. If the medium is idle, the STA resumes the count-down. If theback-off timer reaches 0, the STA may determine a transmission bandwidthby checking whether the secondary channel is idle or busy at thecorresponding time point.

For example, the STA may monitor a channel-idle state during apredetermined IFS (e.g., DIFS or AIFS[i]) on the primary channel anddetermine a transmission start timing on the primary channel by therandom back-off procedure. If the secondary channel is idle during aPIFS shortly before the determined transmission start timing of theprimary channel, the STA may transmit a frame on the primary channel andthe secondary channel.

As described above, when the back-off timer reaches 0 for the primarychannel, the STA may transmit an X-MHz mask PPDU (e.g., where X is 20,40, 80, or 160) on channels including an idle secondary channel(s)according to the CCA result of the secondary channel(s).

The X-MHz mask PPDU is a PPDU for which a TXVECTOR parameter,CH_BANDWIDTH, is set to CBW X. That is, if the X-MHz mask PPDU can betransmitted, this means that a PPDU satisfying a spectrum mask for X-MHztransmission can be transmitted. The X-MHz mask PPDU may include a PPDUtransmitted in a bandwidth equal to or smaller than X MHz.

For example, if an 80-MHz mask PPDU can be transmitted, this means thata PPDU having a channel width of 80 MHz or a PPDU having a channel widthsmaller than 80 MHz (e.g., 40 MHz, 20 MHz, etc.) can be transmittedwithin a Power Spectral Density (PSD) limit of a spectrum mask for80-MHz transmission.

As described before, if a STA is allowed to start a TXOP and has atleast one MAC Service Data Unit (MSDU) to be transmitted under theAccess Category (AC) of the TXOP allowed for the STA, the STA mayperform one of the following a), b), c), d), or e) (in the followingdescription, FIGS. 16 and 17 may be referred to for a primary channel(i.e., a primary 20-MHz channel) a secondary channel (i.e., a secondary20-MHz channel), a secondary 40-MHz channel, and a secondary 80-MHzchannel).

a) If the secondary channel, the secondary 40-MHz channel, and thesecondary 80-MHz channel are idle during a PIFS shortly before the startof the TXOP, a 160-MHz or 80+80-MHz mask PPDU may be transmitted.

b) If both the secondary channel and the secondary 40-MHz channel areidle during the PIFS shortly before the start of the TXOP, an 80-MHzmask PPDU may be transmitted on a primary 80-MHz channel.

c) If the secondary channel is idle during the PIFS shortly before thestart of the TXOP, a 40-MHz mask PPDU may be transmitted on a primary40-MHz channel.

d) A 20-MHz mask PPDU may be transmitted on the primary 20-MHz channel.

e) A channel access attempt may be resumed by performing a back-offprocedure as in the case where the medium is indicated as busy on theprimary channel by one of physical carrier sensing and virtual carriersensing and a back-off timer has a value of 0.

FIGS. 18 and 19 are block diagrams of a transmitting signal processingunit for wideband PPDU transmission.

Wideband PPDU transmission refers to transmission of a PPDU having thesize of a frequency unit for transmission signal processing exceeding apredetermined threshold. For example, if the size of the frequency unitfor transmission signal processing exceeds 80 MHz, transmission of thePPDU may be wideband PPDU transmission. More specifically, wideband PPDUtransmission may include contiguous 160-MHz PPDU or 80+80-MHz PPDUtransmission.

FIG. 18 is a block diagram of the transmitting signal processing unitfor a Data field of a 160-MHz HE Single User (SU) PPDU to which BCCencoding is applied, and FIG. 19 is a block diagram of the transmittingsignal processing unit for a Data field of a 80+80-MHz HE SU PPDU towhich BCC encoding is applied.

The block diagrams of the transmitting signal processing unit 100illustrated in FIGS. 18 and 19 may be specific examples of the blockdiagram of the transmitting signal processing unit 100 illustrated inFIG. 2. For example, the description of the encoder 110, the interleaver120, the mapper 130, the IFT 140, the GI inserter 150, and the RFtransmitter 21 is applicable to BCC encoders 112, BCC interleavers 122,constellation mappers 132, Inverse Discrete Fourier Transformer (IDFTs)142, GI insertion and windowing units 152, and analog and RF units 154illustrated in FIGS. 18 and 19. As described before with reference toFIG. 2, the transmitting signal processing unit 100 may further includea scrambler 104, an encoder parser (e.g., a BCC encoder parser 106), astream parser 114, an STBC encoder 135, CSD per Space Time Stream (STS)inserters 136, and a spatial mapper 138. The same description as givenof FIG. 2 is not provided for the example block diagrams of thetransmitting signal processing unit 100 illustrated in FIGS. 18 and 19.

Additionally, the transmitting signal processing unit 100 may furtherinclude a PHY padder 102 and segment parsers 116 in the examples ofFIGS. 18 and 19. In the case of contiguous 160-MHz transmission asillustrated in the example of FIG. 18, the transmitting signalprocessing unit 100 may further include segment deparsers 134.

Now, a description will be given of operations of the transmittingsignal processing unit 100 with reference to FIGS. 18 and 19.

The PHY padder 102 may add a PAD (i.e., PHY padding bits) and a TAIL(i.e., PPDU TAIL bits) to a Data field or a PSDU of a HE-DATA field, asdescribed before with reference to FIGS. 6 and 7.

The scrambler 104 may scramble data to which the PHY padding is applied.

The BCC encoder parser 106 may divide the scrambled bits among the BCCencoders 112 by providing the scrambled bits to the different BCCencoders 112 in a round robin manner. The number of BCC encoders 112 maybe determined according to rate-dependent parameters (e.g., the numberN_(SYM) of symbols in the Data field, the number N_(DBPS) of data bitsper symbol, etc.).

The stream parser 114 may rearrange the outputs of the BCC encoders 112in blocks. Specifically, the stream parser 114 may divide input bits(i.e., encoded bits) to be transmitted to each user into spatialstreams.

For contiguous 160-MHz or non-contiguous 80+80-MHz transmission, thesegment parsers 116 may divide output bits of the stream parser 114 intotwo frequency subblocks.

The BCC interleavers 122 may interleave bit streams output from thesegment parsers 116.

The constellation mappers 132 may map bit streams output from the BCCinterleavers 122 to Binary Phase Shift Keying (BPSK), Quadrature PSK(QPSK), 16-ary Quadrature Amplitude Modulation (16-QAM), 64-QAM, or256-QAM constellation points.

The segment deparsers 134 may merge the two frequency subblocks into onefrequency segment, for contiguous 160-MHz transmission (e.g., in theexample of FIG. 18). The merged frequency segment may be processed bythe STBC encoder 135, the CSD per STS inserters 136, the spatial mapper138, the IDFTs 142, the GI insertion and windowing units 152, and theanalog and RF units 154. On the other hand, for non-contiguous 80+80-MHztransmission, each frequency subblock may be processed in parallel bythe STBC 135, the CSD per STS inserters 136, the spatial mapper 138, theIDFTs 142, the GI insertion and windowing units 152, and the analog andRF units 154, without merging the frequency subblocks.

The STBC encoder 134 may spread a Spatial Stream (SS) to an STS.

While not shown in the examples of FIGS. 18 and 19, pilot tones may beinserted at specific subcarrier positions.

The CSD per STS inserters 136 may insert a CSD into each STS andfrequency segment.

The spatial mapper 138 may map STSs to transmission chains using aspatial mapping/steering matrix (e.g., matrix Q with N_(TX) rows andN_(STS,total) columns where N_(TX) is the number of transmission chainsand N_(STS,total) is the total number of STSs).

While not shown in FIGS. 18 and 19, appropriate phase rotation may beapplied to each 20-MHz channel.

The IDFTs 142 may calculate an IDFT result for each transmission chainand convert the IDFT result to symbols for the transmission chain. Fornon-contiguous 80+80-MHz transmission as in the example of FIG. 19, eachfrequency subblock may be mapped to a separate IDFT and an IDFT resultmay be calculated.

The GI insertion and window units 152 may insert a GI before a symboland apply windowing to an edge of the symbol.

The analog and RF units 154 may upconvert a complex baseband waveform toan RF signal according to the center frequency of an intended channel,for each transmission chain and transmit the RF signal.

While BCC encoding is used in the examples of FIGS. 18 and 19, theexamples of the present disclosure also include a case in which LDPCencoding is applied instead of BCC encoding. If LDPC encoding isapplied, LDPC encoders may be included instead of the BCC encoder parser106 and the BCC encoders 112. That is, data scrambled by the scrambler104 may be encoded in the LDPC encoders. The LDPC-coded bits may berearranged on a block (or subblock) basis in the stream parser 114 andthe segment parsers 116 (or in the stream parser 114 with the segmentparsers 116 bypassed) and input to the constellation mappers 132. Thatis, unlike the examples of FIGS. 18 and 19, if LDPC encoding is applied,the BCC interleavers 122 may be omitted. Also, if LDPC encoding isapplied, LDPC tone mapping may be applied to constellation-mapped blocks(or subblocks) output from the constellation mappers 132. After the LDPCtone mapping, the LDPC-tone-mapped blocks (or subblocks) may beprocessed by the STBC encoder 135, the CSD per STS inserters 136, thespatial mapper 138, the IDFTs 142, the GI insertion and windowing units152, and the analog and RF units 154 (when needed, after beingprocessing in the segment deparsers 134).

FIG. 20 is a flowchart depicting a method for processing a transmissionsignal for wideband PPDU transmission according to an example of thepresent disclosure.

In step S2010, a transmitting device may perform stream paring on databit streams encoded and output by encoders (for example, BCC encoders orLDPC encoders) of the transmitting device.

In step S2020, the transmitting device may determine whether to performsegment parsing on blocks output through stream parsing based on whethera predetermined condition is satisfied. For example, the predeterminedcondition may be set based on one or more of a PPDU transmissionbandwidth, the size of a frequency unit for transmission signalprocessing, a PPDU type, and use or non-use of OFDMA. Therefore, thetransmitting device may determine whether to perform segment parsing onthe blocks output through stream parsing based on one or more of thePPDU transmission bandwidth, the size of a frequency unit fortransmission signal processing, the PPDU type, and use or non-use ofOFDMA. If a full band channel is divided into a plurality of subchannelsand the subchannels are allocated to a plurality of STAs, this case maycorrespond to use of OFDMA. If a full band channel is not divided into aplurality of subchannels and allocated to one STA, this case maycorrespond to non-use of OFDMA. If a full band channel is not dividedinto a plurality of subchannels and is allocated to a plurality of STAs,for MU-MIMO, this case may also correspond to non-use of OFDMA. The fullband channel may be a 20-MHz channel, a 40-MHz channel, an 80-MHzchannel, an 80+80-MHz channel, or a 160-MHz channel.

If segment parsing is applied, the transmitting device may divide theblocks output through stream parsing into a plurality of subblocks instep S2030. In step S2040, the transmitting device may process theplurality of segment-parsed subblocks, inclusive of constellationmapping.

On the other hand, if segment parsing is not applied, the transmittingdevice goes from step S2020 to step S2040 in which the transmittingdevice may process the plurality of segment-parsed subblocks, inclusiveof constellation mapping.

While not shown in FIG. 20, PHY padding, scrambling, etc. may further beperformed before step S2010. In addition, BCC interleaving (in the caseof BCC encoding), constellation mapping, LDPC tone mapping (in the caseof LDPC encoding), segment deparsing (when needed), STBC encoding, CSDinsertion, spatial mapping, IDFT, CI insertion and windowing, and RFsignal conversion may further be performed in step S2040 (refer to thedescription of FIGS. 2, 18, and 19).

As described in relation to step S2020 of FIG. 20, whether to performsegment parsing (or whether to apply the segment parsers 116) may bedetermined according to a predetermined condition in an example of thepresent disclosure. The predetermined condition may be set based on oneor more of whether the size of a frequency unit for transmission signalprocessing is equal to or less than a predetermined threshold (e.g., YMHz), a PPDU type, and use or non-use of OFDMA.

For example, it may be configured that if the size of the frequency unitfor transmission signal processing is equal to or less than Y MHz,segment parsing is not applied, and if the size of the frequency unitfor transmission signal processing is larger than Y MHz, segment parsingis applied.

Specifically, on the assumption that Y=80, if the size of the frequencyunit for transmission signal processing is equal to or less than 80 MHz,segment parsing may not be applied, and if the size of the frequencyunit for transmission signal processing is larger than 80 MHz (i.e.,wideband PPDU transmission), segment parsing may be applied. Forexample, segment parsing may not be applied to 20-MHz, 40-MHz, or 80-MHzPPDU transmission, whereas segment parsing may be applied to 100-MHz,120-MHz, 160-MHz, 80+20-MHz, 80+40-MHz, or 80+80-MHz PPDU transmission.

More specifically, even in wideband PPDU transmission (e.g., 100-MHz,120-MHz, 160-MHz, 80+20-MHz, 80+40-MHz, or 80+80-MHz PPDU transmission),the size of a frequency unit for transmission signal processing exceeds80 MHz and thus segment parsing is applied in SU transmission or MU-MIMOtransmission. On the contrary, the size of a frequency unit fortransmission signal processing may be equal to or less than 80 MHz inOFDMA transmission.

If SU or MU-MIMO transmission is performed for wideband PPDUtransmission, bits corresponding to, for example, a 160-MHz or 80+80-MHzfrequency unit may be processed by PHY padding, scrambling, FEC encoding(e.g., BCC encoding or LDPC encoding), and stream parsing. That is, inthe case of wideband SU/MU-MIMO PPDU transmission, the size of afrequency unit for transmission signal processing exceeds 80 MHz.

Meanwhile, if OFDMA transmission is performed in wideband PPDUtransmission, PHY padding, scrambling, FEC encoding, and streamingparsing are performed on bits corresponding to a frequency unit having asubchannel bandwidth (e.g., 5 MHz, 10 MHz, 20 MHz, 40 MHz, or 80 MHz).That is, in the case of wideband OFDMA PPDU transmission, the size of afrequency unit for transmission signal processing is equal to or lessthan 80 MHz.

For example, if the bandwidths of four subchannels are 40 MHz, 40 MHz,40 MHz, and 40 MHz in 160-MHz or 80+80-MHz PPDU transmission, the sizesof frequency units for transmission signal processing are 40 MHz, 40MHz, 40 MHz, and 40 MHz (i.e., equal to or less than 80 MHz), and thussegment parsing may not be applied. Or if the bandwidths of foursubchannels are 80 MHz, 40 MHz, 20 MHz, and 20 MHz, respectively in160-MHz or 80+80-MHz PPDU transmission, the sizes of frequency units fortransmission signal processing are 80 MHz, 40 MHz, 20 MHz, and 20 MHz(i.e., equal to or less than 80 MHz), and thus segment parsing may notbe applied.

Also, while segment parsing may be applied to a PPDU type (e.g., a HEPPDU type or a VHT PPDU type) supporting wideband PPDU transmission,segment parsing may not be applied to a PPDU type (e.g., a non-HT PPDUtype, a HT-mixed PPDU type, or a HT-greenfield PPDU type) not supportingwideband PPDU transmission. More specifically, segment parsing may beapplied to a PPDU type (e.g., the VHT PPDU type) not supporting OFDMAtransmission, whereas segment parsing may not be applied to a PPDU type(the HE PPDU type) supporting OFDMA transmission, among the PPDU typessupporting wideband PPDU transmission. That is, while segment parsingmay be applied to a PPDU type supporting only SU transmission or MU-MIMOtransmission (e.g., the VHT PPDU type), segment parsing may not beapplied to a PPDU type supporting SU transmission, MU-MIMO transmission,or OFDMA transmission (e.g., the HE PPDU type).

More specifically, in 160-MHz OFDMA PPDU transmission, segment parsingmay not be applied to transmission on a subchannel of a bandwidth equalto or less than Y MHz (e.g., 20 MHz, 40 MHz, or 80 MHz) (i.e., if thesize of a frequency unit for transmission signal processing is equal toor less than Y MHz), whereas segment parsing may be applied totransmission on a subchannel of a bandwidth larger than Y MHz (e.g., 100MHz, 120 MHz, or 160 MHz) (i.e., if the size of the frequency unit fortransmission signal processing is larger than Y MHz).

As described above, the transmitting device may determine whether toperform or bypass segment parsing in processing a transmission signal,based on one or more of a PPDU transmission bandwidth, the size of afrequency unit for transmission signal processing, a PPDU type, and useor non-use of OFDMA.

If segment parsing is applied, the segment parsers 116 may divide outputbits of the stream parser 114 into two subblocks, as illustrated in theexamples of FIGS. 18 and 19.

Specifically, the stream parser 114 may process data bit streamsreceived from the FEC encoders (e.g., the BCC encoders 112 or LDPCencoders) in N_(CBPS)-bit groups. Each of the groups (that is, N_(CBPS)bits) may be rearranged in N_(SS) blocks, and one block may includeN_(CBPSS) bits (in the case of MU transmission, each group may berearranged in N_(SS,u) blocks, each block including N_(CBPSS,u) bits).Herein, N_(CBPS) represents the number of coded bits per symbol,N_(CBPSS) represents the number of code bits per symbol per spatialstream, N_(CBPSS,u) represents N_(CBPSS) for a specific user, N_(SS)represents the number of spatial streams, and N_(SS,u) represents thenumber of spatial streams for a specific user.

If the segment parsers 116 are applied to output bits of the streamparser 114, each block may be divided into two subblocks. That is,segment parsing is a process of dividing the N_(CBPSS) bits of eachblock into two frequency subblocks each including N_(CBPSS)/2 bits,expressed as

$\begin{matrix}{{y_{k,l} = x_{{{2{s \cdot N_{ES}}{\lfloor\frac{k}{s \cdot N_{ES}}\rfloor}} + {l \cdot s \cdot N_{ES}} + {k\mspace{11mu}{{mod}{({s \cdot N_{ES}})}}}}\;}},{k = 0},1,\ldots\mspace{14mu},{\frac{N_{CBPSS}}{2} - 1}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In [Equation 1], ℑ ┘ represents a floor operation and ℑz┘ is a largestinteger equal to or less than z. z mod t represents the remainder ofdividing integer z by integer t. x_(m) represents an m^(th) bit of ablock including N_(CBPSS) bits (m=0, 1, . . . , N_(CBPSS)−1). l is theindex of a frequency subblock, which is 0 or 1 (if l=0, this indicatessubblock 0 (or a first subblock), and if l=1, this indicates subblock 1(or a second subblock). y_(k,l) represents bit k of frequencysubblock 1. N_(ES) is the number of BCC encoders and s is defined as[Equation 2].

$\begin{matrix}{s = {\max\left\{ {1,\frac{N_{BPSCS}}{2}} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In [Equation 2], N_(BPSCS) is the number of coded bits per subcarrierper spatial stream, and max{a,b} represents the larger value between aand b.

If segment parsing is not applied (i.e., the segment parsers 116 arebypassed), the bits (i.e., N_(CBPSS) bits) of one block output from thestream parser 114 may be said to be mapped to one subblock. This may beexpressed as [Equation 3].y _(k,l) =x _(k) , k=0, 1, . . . , N _(CBPSS)  [Equation 3]

In [Equation 3], l represents the index of a frequency subblock and l=0.That is, only the first subblock is assumed, while the second subblockis not assumed. x_(m) represents an m^(th) bit of a block havingN_(CBPSS) bits, and m=0, 1, . . . , N_(CBPSS)−1. y_(k,l) represents bitk of frequency subblock l.

FIG. 21 is a flowchart depicting a method for processing a receivedsignal, for wideband PPDU reception according to an example of thepresent disclosure.

Basically, the operation for processing a received wideband PPDU signalillustrated in FIG. 21 may have a reciprocal relationship with theoperation for processing a wideband PPDU transmission signal illustratedin FIG. 20.

In step S2110, a receiving device may perform STBC decoding onconstellation points of an STS output from a spatial demapper, fordespreading the STS to a spatial stream.

In step S2120, the receiving device may determine whether to performsegment parsing on a constellation-point block output from an STBCdecoder, depending on whether a predetermined condition is satisfied.For example, the predetermined condition may be set based on one or moreof a PPDU reception bandwidth, the size of a frequency unit forreception signal processing, a PPDU type, and use or non-use of OFDMA.Therefore, the receiving device may determine whether to perform segmentparsing on the constellation-point block output from the STBC decoder,based on one or more of the PPDU reception bandwidth, the size of thefrequency unit for reception signal processing, the PPDU type, and useor non-use of OFDMA.

As described before, when processing a transmission signal, thetransmitting device may apply segment parsing according to whether apredetermined condition regarding a PPDU transmission bandwidth, thesize of a frequency unit for transmission signal processing, a PPDUtype, or use or non-use of OFDMA is satisfied, and then perform segmentdeparsing after constellation-point mapping. Similarly, the receivingdevice may apply segment parsing and segment deparsing to thetransmission signal to which segment parsing and segment deparsing havebeen applied, depending on a condition corresponding to thepredetermined condition (i.e., a PPDU reception bandwidth, the size of afrequency unit for reception signal processing, a PPDU type, or use ornon-use of OFDMA) is satisfied.

If segment parsing is applied, the receiving device may divide aconstellation-point block output from the STBC decoder into a pluralityof subblocks in step S2130. The plurality of segment-parsed subblocksmay be subject to processes including constellation demapping in stepS2140.

If segment parsing is not applied, the receiving device may proceeddirectly to step S2140 in which a constellation-point block output fromthe STBC decoder may be subject to processes including constellationdemapping.

While not shown in FIG. 21, a step for receiving an RF signal,converting the RF signal to one or more symbols, removing GIs from theone or more symbols, performing Fourier transform on the GI-removedsymbols, performing spatial demapping on the Fourier-transformedsymbols, and converting the symbols to frequency-domain constellationpoints by removing CSDs may further be performed before step S2110.

Also, the receiving device may further perform a step for generating aplurality of subblocks through LDPC tone demapping (if the receivedsignal is an LDPC-encoded signal), constellation demapping, BCCdeinterleaving (if the received signal is a BCC-encoded signal), andsegment deparsing (when needed), generating a block through streamdeparsing of the plurality of subblocks, and merging streams in stepS2140. Further, a stream output from the stream deparser may be decodedby an FEC decoder (for example, a BCC decoder or an LDPC decoder), thedecoded data may be descrambled, and a PHY padding may be removed fromthe descrambled data.

FIGS. 22 and 23 depict example HE PPDU formats in the case where OFDMAtransmission is performed using a wideband channel bandwidth.

The example of FIG. 22 illustrates a case in which an AP allocates a20-MHz subchannel to each of STA1, STA2, STA3, STA4, STA5, STA6, STA7,and STA8 and transmits data units simultaneously to STA1, STA2, STA3,STA4, STA5, STA6, STA7, and STA8 on the allocated 20-MHz subchannels. Inthe example of FIG. 22, PSDU transmission time points are identical onthe plurality of subchannels (e.g., the lengths of HE-LTF sections areequal on the plurality of subchannels). That is, the example of FIG. 22is an extension of the examples in which PSDU transmission time pointsare identical on a plurality of subchannels within one 20-MHz channel,among the examples described before with reference to FIGS. 8 to 15, toa plurality of 20-MHz channels. The description of OFDMA transmission ona plurality of subchannels within a 20-MHz channel may be extended toPPDU transmission in a 160-MHz or 80+80-MHz channel bandwidth, and each20-MHz channel may have the same OFDM symbol duration and the same GI.

The example of FIG. 23 illustrates a case in which an AP allocates a20-MHz subchannel to each of STA1, STA2, STA3, STA4, STA5, STA6, STA7,and STA8 and transmits data units simultaneously to STA1, STA2, STA3,STA4, STA5, STA6, STA7, and STA8 on the allocated 20-MHz subchannels. Inthe example of FIG. 23, PSDU transmission time points are not identicalon the plurality of subchannels (e.g., the lengths of HE-LTF sectionsare not equal on the plurality of subchannels). That is, the example ofFIG. 23 is an extension of the examples in which PSDU transmission timepoints are not identical on a plurality of subchannels within one 20-MHzchannel, among the examples described before with reference to FIGS. 8to 15, to a plurality of 20-MHz channels. The description of OFDMAtransmission on a plurality of subchannels within a 20-MHz channel inthese examples may be extended to PPDU transmission in a 160-MHz or80+80-MHz channel bandwidth, and each 20-MHz channel may have the sameOFDM symbol duration and the same GI.

As in the examples of FIGS. 22 and 23, it may be assumed that a widebandchannel bandwidth (e.g., a 160-MHz or 80+80-MHz channel bandwidth) isdivided into a plurality of subchannels, the plurality of subchannelsare allocated to a plurality of STAs, and simultaneous transmission(i.e., OFDMA HE PPDU transmission) to the STAs is performed.

On the other hand, unlike the examples of FIGS. 22 and 23, it may beassumed that if a wideband channel width (160 MHz or 80+80 MHz) isallocated only to one STA and a wideband HE PPDU is transmitted to theSTA (i.e., SU PPDU transmission), or an equal channel bandwidth isallocated to each of a plurality of STAs and different spatial streamsare allocated and transmitted simultaneously to the STAs (i.e., MU-MIMOPPDU transmission).

In the case of wideband (e.g. 160 MHz or 80+80 MHz) SU/MU-MIMO PPDUtransmission, bits output from the stream parser 114 may be divided intoa plurality of frequency subblocks through the segment parsers 116, andthe bits of each frequency subblock may be interleaved through the BCCinterleavers 122, converted through the constellation mappers 132, andthen transmitted (or, if LDPC encoding is applied, the bits output fromthe stream parser 114 may be divided into the plurality of frequencysubblocks through the segment parsers 116, and the bits of eachfrequency subblock may be converted through the constellation mappers132, and then transmitted (the BCC interleavers 122 are omitted)).

In the case of wideband (e.g. 160 MHz or 80+80 MHz) OFDMA PPDUtransmission, bits output from the stream parser 114 may be interleavedthrough the BCC interleavers 122 and converted through the constellationmappers 132, for each of subchannels allocated to a plurality of STAs,and then transmitted (or, if LDPC encoding is applied, the bits outputfrom the stream parser 114 may be converted through the constellationmappers 132, LDPC-tone-mapped, and then transmitted).

As described above, the segment parsers 116 may be used for widebandSU/MU-MIMO PPDU transmission, whereas the segment parsers 116 may not beused for wideband OFDMA PPDU transmission.

That is, in wideband SU/MU-MIMO PPDU transmission, bits output from thestream parser 114 may be divided into a plurality of frequency subblocksin the segment parsers 116, and the frequency subblocks may be convertedin the constellation mappers 132 and then transmitted.

On the other hand, in wideband OFDMA PPDU transmission, bits output fromthe stream parser 114 may be converted directly in the constellationmappers 132 and then transmitted. In 160-MHz or 80+80-MHz OFDMA PPDUtransmission, bits output from the stream parser 114 may be configuredseparately for the respective subchannels. Specifically, the streamparser 114 may divide input bits (i.e., encoded bits) to be transmittedto each user into spatial streams. More specifically, the single streamparser 114 may receive bits distinguished from each other for therespective subchannels, and divide input bits for each subchannel intospatial streams.

For example, if a 160-MHz channel bandwidth is allocated to one STA, fortransmission, the segment parsers 116 may be used. On the other hand, ifa 160-MHz channel bandwidth is divided into a plurality of subchannelsand the subchannels are allocated to a plurality of STAs, forsimultaneous transmission, the segment parsers 116 may not be used.

FIG. 24 depicts an example channel access operation for wideband OFDMAPPDU transmission.

In the example of FIG. 24, a backoff operation may be performed on aprimary channel. Upon expiration of a backoff timer, the CCA states of asecondary 20-MHz channel, a secondary 40-MHz channel, and a secondary80-MHz channel are monitored during a PIFS. Then, an HE PPDUtransmission bandwidth may be determined for an idle-state secondarychannel.

That is, as in the examples of determining a transmission bandwidth (ora transmission channel width) by a STA following a contention-basedchannel access scheme (e.g., EDCA), described before with reference toFIGS. 16 and 17, if a STA is allowed to start a TXOP and has at leastone MSDU to be transmitted for the AC of the allowed TXOP, the STA mayperform one of a), b), c), d), and e). As defined for 160-MHz or80+80-MHz mask PPDU transmission in a), if the secondary channel, thesecondary 40-MHz channel, and the secondary 80-MHz channel are idleduring a PIFS shortly before the start of the TXOP, a 160-MHz or80+80-MHz mask PPDU may be transmitted.

As illustrated in the example of FIG. 24, if wideband (e.g., 160-MHz or80+80-MHz) HE PPDU transmission is possible, an AP may determine whetherto transmit a wideband HE PPDU by allocating a wideband PPDUtransmission bandwidth to one or more STAs in a SU or MU-MIMOtransmission scheme, or by allocating a plurality of subchannels to aplurality of STAs in an OFDMA transmission scheme.

If the wideband HE PPDU is transmitted in the SU/MU-MIMO transmissionscheme, a PSDU may be divided into a plurality of subblocks (e.g., twosubblocks) using segment parsers and then transmitted.

On the other hand, If the wideband HE PPDU is transmitted in the OFDMAtransmission scheme, PSDUs may be divided into subchannels (or frequencysubblocks) for a plurality of respective STAs without using segmentparsers and then transmitted.

In the example of FIG. 24, an AP transmitting a wideband HE PPDUallocates a 20-MHz subchannel, a 20-MHz subchannel, a 40-MHz subchannel,and an 80-MHz subchannel respectively to STA1, STA2, STA3, and STA4 andsimultaneously transmit PSDUs to STA1, STA2, STA3, and STA4 on theallocated subchannels. Segment parsing is not performed on the PSDUtransmitted to each of the STAs.

FIG. 25 is a flowchart depicting a method for determining a transmissionbandwidth for wideband PPDU transmission according to an example of thepresent disclosure.

The foregoing examples are based on the assumption that when a HE PPDUis transmitted in a wideband transmission bandwidth (e.g., a channelbandwidth exceeding 80 MHz), a contiguous 160-MHz or non-contiguous80+80-MHz channel bandwidth is used. Now, a description will be given ofa method for supporting transmission of a HE PPDU with a channelbandwidth exceeding 80 MHz, when only a part of a secondary 80-MHzchannel is idle according to an additional example of the presentdisclosure.

For example, if the primary channel, the secondary 20-MHz channel, andthe secondary 40-MHz channel are idle, a contiguous 100-MHz (ornon-contiguous 80+20-MHz), contiguous 120-MHz (or non-contiguous80+40-MHz), or contiguous 160-MHz (or non-contiguous 80+80-MHz) maskPPDU may be transmitted depending on whether the whole or a part offrequency segments of the secondary 80-MHz channel are idle.

That is, only a 160-MHz or 80+80-MHz channel bandwidth may be supportedas a wideband transmission bandwidth, while a 100-MHz, 80+20-MHz,120-MHz, or 80+40-MHz channel bandwidth may not be supported as awideband transmission bandwidth in the channel access scheme describedbefore with reference to FIG. 16, 17, or 24. However, a 100-MHz,80+20-MHz, 120-MHz, 80+40-MHz, 160-MHz, or 80+80-MHz channel bandwidthmay be supported as a wideband transmission bandwidth in the additionalexample of the present disclosure. Therefore, the use efficiency ofchannel resources can be increased.

Hereinafter, a method for determining a HE PPDU transmission bandwidthaccording to an additional example of the present disclosure will bedescribed in detail with reference to FIG. 25.

In the example of FIG. 25, upon generation of a transmission frame, atransmitting device may determine a transmission bandwidth (or atransmission channel width) according to a contention-based channelaccess scheme (e.g., EDCA).

In step S2510, the transmitting device may start a backoff procedure onthe primary channel to acquire a TXOP. Specifically, after thetransmitting device determines that the CCA state of the primary channelis idle by sensing the primary channel during a time interval of a DIFSor AIFS[i], the transmitting device may start the backoff procedureaccording to a selected random backoff count.

In step S2520, the transmitting device may determine whether the CCAstate of the primary channel is idle or busy during a time periodcorresponding to one backoff slot. If the CCA state of the primarychannel is the idle state, the transmitting device may count down thebackoff timer by 1 in step S2522 and determine whether the backoff timerhas expired (i.e., the backoff timer has reached 0) in step S2524. Ifthe CCA state of the primary channel is the busy state, the transmittingdevice may stop the count-down and wait in step S2526 and return to stepS2520 in which the transmitting device may determine again whether theprimary channel is idle.

If the transmitting device determines that the backoff timer has reached0 in step S2522, the transmitting device may determine whether the CCAstate(s) of secondary channel(s) are the idle or busy state at acorresponding time point (i.e., a starting transmission timing) in stepS2530. Specifically, once the starting transmission timing is determinedfor the primary channel, the transmitting device may determine whetherthe CCA state(s) of the secondary channel(s) are the idle state during aPIFS shortly before the starting transmission timing.

In step S2540, the transmission bandwidth may be determined based on theCCA state(s) of the secondary channel(s) determined in step S2530. Morespecifically, if the transmitting device is allowed to start a TXOP andhas at least one MSDU to be transmitted for the AC of the allowed TXOP,the transmitting device may determine a transmission bandwidth byperforming one of the following a1), a2), a3), b), c), d), and e).

a1) If the secondary channel, the secondary 40-MHz channel, and thesecondary 80 MHz in 80-MHz channel are idle during a PIFS shortly beforethe start of a TXOP, a 160-MHz or 80+80-MHz mask PPDU may betransmitted.

a2) If the secondary channel, the secondary 40-MHz channel, and thesecondary 40 MHz in 80-MHz channel are idle during a PIFS shortly beforethe start of a TXOP, a 120-MHz or 80+40-MHz mask PPDU may betransmitted.

a3) If the secondary channel, the secondary 40-MHz channel, thesecondary 40 MHz in 80-MHz channel, and the secondary 20 MHz in 80-MHzchannel are idle during a PIFS shortly before the start of a TXOP, a100-MHz or 80+20-MHz mask PPDU may be transmitted.

b) If both the secondary channel and the secondary 40-MHz channel areidle during a PIFS shortly before the start of a TXOP, an 80-MHz maskPPDU may be transmitted on the primary 80-MHz channel.

c) If the secondary channel is idle during a PIFS shortly before thestart of a TXOP, a 40-MHz mask PPDU may be transmitted on the primary40-MHz channel.

d) A 20-MHz mask PPDU may be transmitted on the primary 20-MHz channel.

e) A channel access attempt may be re-started by performing a backoffprocedure, as in the case where a medium on a primary channel isindicated as busy by one of physical carrier sensing and virtual carriersensing and a backoff timer has a value of 0.

In step S2550, an X-MHz mask PPDU (e.g., X=20, 40, 80, 100, 120, or 160)may be transmitted on the primary channel and the secondary channel(s)determined to be idle in step S2530.

Meanwhile, similarly to the description of FIG. 10, if a HE PPDUtransmission channel is configured with non-contiguous channels (e.g.,non-contiguous 80+20 MHz, non-contiguous 80+40 MHz, or non-contiguous80+80 MHz) in HE PPDU transmission using the whole or a part offrequency segments of the secondary 80-MHz channel, no subchannel may beallocated with overlap between the plurality of non-contiguous channels.That is, if the HE PPDU transmission channel includes non-contiguousfirst and second channels, one subchannel may not be allocated across apart of the first channel and a part of the second channel.

For example, if two 80-MHz channels are non-contiguous in FIG. 24, theAP may not allow allocation of the secondary 40-MHz channel and thesecond 40 MHz in 80 MHz channel to allocate an 80-MHz subchannel toSTA3.

FIG. 26 depicts another example of a channel access operation forwideband OFDMA PPDU transmission.

While the AP monitors the CCA state of the whole secondary 80-MHzchannel during a PIFS shortly before a starting transmission timing(i.e., a time point at which a backoff timer has expired on the primarychannel) in the example of FIG. 24, the AP monitors the CCA states ofthe secondary 20 MHz in 80-MHz channel, the secondary 40 MHz in 80-MHzchannel, and the secondary 80 MHz in 80-MHz channel, separately in theexample of FIG. 26. A HE PPDU transmission bandwidth that the APdetermines based on the CCA state of each of the frequency segments ofthe secondary 80-MHz channel may be 100 MHz, 120 MHz, or 160 MHz.

To determine the CCA states of the secondary 20 MHz in 80-MHz channel,the secondary 40 MHz in 80-MHz channel, and the secondary 80 MHz in80-MHz channel, CCA bitmap information about the frequency segments ofthe secondary 80-MHz channel may be used. Specifically, the CCA bitmapinformation may include 4 bits indicating the respective four 20-MHzchannels of the secondary 80-MHz channel (i.e., the frequency segmentsof the secondary 80-MHz channel). For example, the first, second, third,and fourth bit positions of the 4-bit bitmap may indicate the CCA states(idle/busy) of the four 20-MHz channels in the order of lowest tohighest frequencies in the secondary 80-MHz channel. If one bit value is0, this may indicate the idle state and if it is 1, this may indicatethe busy state (or if one bit value is 1, this may indicate the idlestate and if it is 0, this may indicate the busy state). For example,the bitmap information may be generated in the PHY and transmitted tothe MAC in the transmitting device transmitting a wideband HE PPDU ormay be generated based on CCA states transmitted from the MAC to the PHYin the transmitting device.

FIG. 26 illustrates an example in which a secondary 80-MHz CCA bitmap isconfigured as {CH1, CH2, CH3, CH4}. It is assumed that four 20-MHzchannels of the secondary 80-MHz channel are indexed with CH1, CH2, CH3,and CH4, respectively in an ascending order of frequency. If thesecondary 40 MHz in 80 MHz channel is idle during a PIFS shortly beforeexpiration of a backoff timer, the secondary 80-MHz CCA bitmap mayindicate {idle, idle, busy, busy}. The AP may determine a transmissionbandwidth for a HE PPDU to be contiguous 120 MHz (or non-contiguous80+40 MHz), using the secondary 80-MHz CCA bitmap.

In the example of FIG. 26, the AP allocates a 20-MHz subchannel, a20-MHz subchannel, a 40-MHz subchannel, and a 40-MHz subchannel,respectively to STA1, STA2, STA3, and STA4 and simultaneously transmitsPSDUs to STA1, STA2, STA3, and STA4. Segment parsing may not beperformed on the PSDU transmitted to each STA.

FIG. 27 is a block diagram of a transmitting signal processing unit forOFDMA PPDU transmission according to the present disclosure.

For example, FIG. 27 may be a block diagram of a transmitting signalprocessing unit in a transmitting STA that divides channel bandwidths of20 MHz, 40 MHz, 80 MHz, 160 MHz into a plurality of subchannels,allocates the subchannels to a plurality of STAs, and simultaneouslytransmits a HE PPDU to the STAs. In FIG. 27, the transmitting STA maybe, for example, an AP.

In FIG. 27, signals are simultaneously transmitted to N_(user) users(e.g., User_0, . . . , User_N_(user)−1). The same encoding scheme ordifferent encoding schemes may be applied to the plurality of users. Forexample, LDPC encoding may be applied to a signal transmitted to each ofthe N_(user) users. Or BCC encoding may be applied to a signaltransmitted to each of the N_(user) users. Or LDPC encoding may beapplied to a part of the N_(user) users, whereas BCC encoding may beapplied to the remaining part of the N_(user) users. For example, LDPCencoding may be applied to a signal transmitted to User_0 and BCCencoding may be applied to a signal transmitted to User_N_(user)−1.

As illustrated in FIG. 27, a plurality of spatial streams may begenerated for each user through processing in the PHY padder 102, thescrambler 104, the BCC encoders 112 or an LDPC encoder 113, and thestream parser 114. The respective spatial streams may be processed inthe constellation mappers 132 and the CSD per STS inserters 136. If theBCC encoders 112 are used, BCC interleaving may be performed beforeconstellation mapping. If the LDPC encoder 113 are used, LDPC tonemapping of LDPC tone mappers 133 may be performed before constellationmapping of the constellation mappers 132.

For example, if LDPC encoding is applied for User_0, LDPC encoded bitsmay be output by processing input bits to be transmitted to User_0 inthe PHY padder 102, the scrambler 104, and the LDPC encoder 113. Aplurality of spatial streams may be generated by processing the LDPCencoded bits in the stream parser 114. That is, a plurality of spatialstreams may be generated for each user. The respective spatial streamsmay be input to segment deparsers 134-1 to 134-n after being processedin the constellation mappers 132, the LDPC tone mappers 133, and the CSDper STS inserters 136. While CSD per STC insertion is not performed onsome stream in the example of FIG. 27, it may be said that a CSD of 0 isinserted in the stream.

For example, if LDPC encoding is applied for User_N_(user)−1, BCCencoded bits may be output by processing input bits to be transmitted toUser_N_(user)−1 in the PHY padder 102, the scrambler 104, the BCCencoder parser 106, and the BCC encoders 112. A plurality of spatialstreams may be generated by processing the BCC encoded bits in a streamparser 116. That is, a plurality of spatial streams may be generated foreach user. The respective spatial streams may be input to the segmentdeparsers 134-1 to 134-n after being processed in the BCC interleavers122, the constellation mappers 132, and the CSD per STS inserters 136.

The segment deparsers 134-1, . . . , 134-n may perform segment deparsingon n respective STSs STS_1, . . . , STS_n. The segment deparsers 134-1,. . . , 134-n may configure one contiguous frequency segment block witha plurality of subchannels allocated to a plurality of users. Once thecontiguous frequency segment block is configured through the segmentdeparsers 134-1, . . . , 134-n, modulated waveforms may be transmittedto the plurality of users (or STAs) by subjecting the respective STSs tospatial mapping, IDFT, GI insertion and windowing, and analog and RFprocessing in the spatial mapper 138, the IDFTs 142, the GI insertionand windowing units 152, and the analog and RF units 154, for a totalchannel bandwidth (e.g., 20 MHz, 40 MHz, 80 MHz, or 160 MHz) in whichthe PPDU is transmitted.

The segment deparsers 134-1, . . . , 134-n may be used in the case wherea 160-MHz channel bandwidth is allocated to one STA, for transmission,and in the case where the 160-MHz channel bandwidth is divided into aplurality of subchannels and the subchannels are allocated to aplurality of STAs, for simultaneous transmission. Although differentimplementation algorithms may be available for the segment deparsers134-1, . . . , 134-n, they are common in that one contiguous frequencysegment block is configured with divided frequency segment blocks.

While the afore-described example methods of the present disclosure havebeen described as a series of operations for simplicity of description,this does not limit the sequence of steps. In some embodiments, stepsmay be performed at the same time or in a different sequence. All of theexample steps are not always necessary to implement the method proposedby the present disclosure.

The foregoing embodiments of the present disclosure may be implementedseparately or combinations of two or more of the embodiments may beimplemented simultaneously, for the afore-described example methods ofthe present disclosure.

The present disclosure includes an apparatus for processing orperforming the method of the present disclosure (e.g., the wirelessdevice and its components described with reference to FIGS. 1, 2, and3).

The present disclosure includes software or machine-executableinstructions (e.g., an operating system (OS), an application, firmware,a program, etc.) for executing the method of the present disclosure in adevice or a computer, and a non-transitory computer-readable mediumstoring the software or instructions that can be executed in a device ora computer.

While various embodiments of the present disclosure have been describedin the context of an IEEE 802.11 system, they are applicable to variousmobile communication systems.

What is claimed is:
 1. A method for transmitting a Physical layerProtocol Data Unit (PPDU) in a wireless local area network, the methodcomprising: determining whether Orthogonal Frequency Division MultipleAccess (OFDMA) is used by the PPDU; selectively performing segmentparsing on blocks received from either a stream parser or a Space-TimeBlock Coding (STBC) decoder based on whether Orthogonal FrequencyDivision Multiple Access (OFDMA) is used by the PPDU, wherein thesegment parsing, when performed, outputs frequency subblocks; andtransmitting the PPDU with the frequency subblocks when segment parsingis performed.
 2. The method according to claim 1, wherein the segmentparsing is further selectively performed based on at least one of atransmission bandwidth of the PPDU, a resource unit size allocated inthe PPDU, and a type of the PPDU.
 3. The method according to claim 2,wherein the segment parsing is bypassed when the transmission bandwidthof the PPDU is equal to or less than 80 MHz.
 4. The method according toclaim 2, wherein the segment parsing is bypassed when a resource unitsize allocated in the PPDU has a size equal to or less than 80 MHz. 5.The method according to claim 1, wherein the segment parsing is bypassedwhen OFDMA is used by the PPDU.
 6. The method according to claim 2,wherein the segment parsing is performed when the transmission bandwidthof the PPDU is greater than 80 MHz, the resource unit size allocated inthe PPDU is greater than 80 MHz, OFDMA is not applied, and the type ofthe PPDU is a Very High Throughput (VHT) PPDU type or a High Efficiency(HE) PPDU type.
 7. The method according to claim 1, further comprising:determining a channel state of each of one or more portions of asecondary channel; and determining a transmission bandwidth for thePPDU, wherein the transmission bandwidth includes at least one of theone or more portions of the secondary channel, and wherein the PPDU istransmitted on the determined transmission bandwidth.
 8. The methodaccording to claim 7, wherein the secondary channel is a secondary 80MHz channel.
 9. The method according to claim 8, wherein thetransmission bandwidth includes a primary channel, a secondary 20 MHzchannel, a secondary 40 MHz channel, and at least one of the one or moreportions of the secondary 80 MHz channel.
 10. The method according toclaim 9, wherein the transmission bandwidth is determined as one ofcontiguous 100 MHz, non-contiguous 80+20 MHz, contiguous 120 MHz,non-contiguous 80+40 MHz, contiguous 160 MHz, or non-contiguous 80+80MHz.
 11. The method according to claim 10, wherein a channel state ofeach portion of the secondary channel is determined during an intervalimmediately preceding a start of a transmission opportunity (TXOP). 12.The method according to claim 11, wherein the TXOP is obtained based ona channel state of a primary channel.
 13. The method according to claim12, wherein the channel state of the primary channel is a Clear ChannelAssessment (CCA) state indicating an idle state or a busy state.
 14. Themethod according to claim 13, wherein the interval corresponds to a PIFS(Point coordination function Inter-Frame Space) time.
 15. Anon-transitory machine-readable storage medium that includesinstructions, which when executed by a processor of a computer system,causes the computer system to: determine whether Orthogonal FrequencyDivision Multiple Access (OFDMA) is used by a Physical layer ProtocolData Unit (PPDU); selectively perform segment parsing on blocks receivedfrom either a stream parser or a Space-Time Block Coding (STBC) decoderbased on whether Orthogonal Frequency Division Multiple Access (OFDMA)is used by the PPDU, wherein the segment parsing, when performed,outputs frequency subblocks; and transmit the PPDU with the frequencysubblocks when segment parsing is performed.
 16. The non-transitorymachine-readable storage medium according to claim 15, wherein thesegment parsing is bypassed when OFDMA is used by the PPDU.
 17. Thenon-transitory machine-readable storage medium according to claim 15,wherein the segment parsing is further selectively performed based on atleast one of a transmission bandwidth of the PPDU, a resource unit sizeallocated in the PPDU, and a type of the PPDU.
 18. A computer systemcomprising: a processor; and a memory unit coupled to the processor,wherein the memory unit includes instructions that when executed by theprocessor cause the computer system to: determine whether OrthogonalFrequency Division Multiple Access (OFDMA) is used by a Physical layerProtocol Data Unit (PPDU); selectively perform segment parsing on blocksreceived from either a stream parser or a Space-Time Block Coding (STBC)decoder based on whether Orthogonal Frequency Division Multiple Access(OFDMA) is used by the PPDU, wherein the segment parsing, whenperformed, outputs frequency subblocks; and transmit the PPDU with thefrequency subblocks when segment parsing is performed.
 19. The computersystem according to claim 18, wherein the segment parsing is bypassedwhen OFDMA is used by the PPDU.
 20. The computer system according toclaim 18, wherein the segment parsing is further selectively performedbased on at least one of a transmission bandwidth of the PPDU, aresource unit size allocated in the PPDU, and a type of the PPDU.